GNAP J. Richer, Ed.
Internet-Draft Bespoke Engineering
Intended status: Standards Track A. Parecki
Expires: 28 March 2022 Okta
F. Imbault
acert.io
24 September 2021
Grant Negotiation and Authorization Protocol
draft-ietf-gnap-core-protocol-07
Abstract
GNAP defines a mechanism for delegating authorization to a piece of
software, and conveying that delegation to the software. This
delegation can include access to a set of APIs as well as information
passed directly to the software.
Status of This Memo
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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Elements . . . . . . . . . . . . . . . . . . . . . . . . 9
1.4. Trust relationships . . . . . . . . . . . . . . . . . . . 10
1.5. Sequences . . . . . . . . . . . . . . . . . . . . . . . . 11
1.5.1. Redirect-based Interaction . . . . . . . . . . . . . 15
1.5.2. User-code Interaction . . . . . . . . . . . . . . . . 18
1.5.3. Asynchronous Authorization . . . . . . . . . . . . . 20
1.5.4. Software-only Authorization . . . . . . . . . . . . . 22
1.5.5. Refreshing an Expired Access Token . . . . . . . . . 23
1.5.6. Requesting User Information . . . . . . . . . . . . . 25
2. Requesting Access . . . . . . . . . . . . . . . . . . . . . . 26
2.1. Requesting Access to Resources . . . . . . . . . . . . . 28
2.1.1. Requesting a Single Access Token . . . . . . . . . . 28
2.1.2. Requesting Multiple Access Tokens . . . . . . . . . . 31
2.2. Requesting Subject Information . . . . . . . . . . . . . 33
2.3. Identifying the Client Instance . . . . . . . . . . . . . 34
2.3.1. Identifying the Client Instance by Reference . . . . 35
2.3.2. Providing Displayable Client Instance Information . . 36
2.3.3. Authenticating the Client Instance . . . . . . . . . 36
2.4. Identifying the User . . . . . . . . . . . . . . . . . . 37
2.4.1. Identifying the User by Reference . . . . . . . . . . 38
2.5. Interacting with the User . . . . . . . . . . . . . . . . 38
2.5.1. Start Mode Definitions . . . . . . . . . . . . . . . 40
2.5.2. Finish Interaction Modes . . . . . . . . . . . . . . 41
2.5.3. Hints . . . . . . . . . . . . . . . . . . . . . . . . 44
2.5.4. Extending Interaction Modes . . . . . . . . . . . . . 44
2.6. Extending The Grant Request . . . . . . . . . . . . . . . 44
3. Grant Response . . . . . . . . . . . . . . . . . . . . . . . 45
3.1. Request Continuation . . . . . . . . . . . . . . . . . . 46
3.2. Access Tokens . . . . . . . . . . . . . . . . . . . . . . 47
3.2.1. Single Access Token . . . . . . . . . . . . . . . . . 48
3.2.2. Multiple Access Tokens . . . . . . . . . . . . . . . 51
3.3. Interaction Modes . . . . . . . . . . . . . . . . . . . . 52
3.3.1. Redirection to an arbitrary URL . . . . . . . . . . . 53
3.3.2. Launch of an application URL . . . . . . . . . . . . 54
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3.3.3. Display of a Short User Code . . . . . . . . . . . . 54
3.3.4. Interaction Finish . . . . . . . . . . . . . . . . . 55
3.3.5. Extending Interaction Mode Responses . . . . . . . . 56
3.4. Returning Subject Information . . . . . . . . . . . . . . 56
3.5. Returning Dynamically-bound Reference Handles . . . . . . 57
3.6. Error Response . . . . . . . . . . . . . . . . . . . . . 58
3.7. Extending the Response . . . . . . . . . . . . . . . . . 59
4. Determining Authorization and Consent . . . . . . . . . . . . 59
4.1. Interaction Start Methods . . . . . . . . . . . . . . . . 62
4.1.1. Interaction at a Redirected URI . . . . . . . . . . . 62
4.1.2. Interaction at the User Code URI . . . . . . . . . . 63
4.1.3. Interaction through an Application URI . . . . . . . 64
4.2. Post-Interaction Completion . . . . . . . . . . . . . . . 64
4.2.1. Completing Interaction with a Browser Redirect to the
Callback URI . . . . . . . . . . . . . . . . . . . . 65
4.2.2. Completing Interaction with a Direct HTTP Request
Callback . . . . . . . . . . . . . . . . . . . . . . 66
4.2.3. Calculating the interaction hash . . . . . . . . . . 66
5. Continuing a Grant Request . . . . . . . . . . . . . . . . . 68
5.1. Continuing After a Completed Interaction . . . . . . . . 70
5.2. Continuing During Pending Interaction . . . . . . . . . . 71
5.3. Modifying an Existing Request . . . . . . . . . . . . . . 73
5.4. Canceling a Grant Request . . . . . . . . . . . . . . . . 78
6. Token Management . . . . . . . . . . . . . . . . . . . . . . 79
6.1. Rotating the Access Token . . . . . . . . . . . . . . . . 79
6.2. Revoking the Access Token . . . . . . . . . . . . . . . . 81
7. Securing Requests from the Client Instance . . . . . . . . . 82
7.1. Key Formats . . . . . . . . . . . . . . . . . . . . . . . 83
7.1.1. Key References . . . . . . . . . . . . . . . . . . . 84
7.2. Presenting Access Tokens . . . . . . . . . . . . . . . . 84
7.3. Proving Possession of a Key with a Request . . . . . . . 85
7.3.1. HTTP Message Signing . . . . . . . . . . . . . . . . 87
7.3.2. Mutual TLS . . . . . . . . . . . . . . . . . . . . . 91
7.3.3. Detached JWS . . . . . . . . . . . . . . . . . . . . 93
7.3.4. Attached JWS . . . . . . . . . . . . . . . . . . . . 97
8. Resource Access Rights . . . . . . . . . . . . . . . . . . . 101
8.1. Requesting Resources By Reference . . . . . . . . . . . . 104
9. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 106
9.1. RS-first Method of AS Discovery . . . . . . . . . . . . . 107
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 109
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 109
12. Security Considerations . . . . . . . . . . . . . . . . . . . 109
12.1. TLS Protection in Transit . . . . . . . . . . . . . . . 109
12.2. Protection of Client Instance Key Material . . . . . . . 110
12.3. Protection of Authorization Server . . . . . . . . . . . 111
12.4. Symmetric and Asymmetric Client Instance Keys . . . . . 112
12.5. Generation of Access Tokens . . . . . . . . . . . . . . 113
12.6. Bearer Access Tokens . . . . . . . . . . . . . . . . . . 114
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12.7. Key-Bound Token Access Tokens . . . . . . . . . . . . . 114
12.8. Exposure of End-user Credentials to Client Instance . . 115
12.9. Mixing Up Authorization Servers . . . . . . . . . . . . 116
12.10. Processing of Client-Presented User Information . . . . 117
12.11. Client Instance Pre-registration . . . . . . . . . . . . 118
12.12. Client Instance Impersonation . . . . . . . . . . . . . 119
12.13. Interception of Information in the Browser . . . . . . . 120
12.14. Callback URL Manipulation . . . . . . . . . . . . . . . 120
12.15. MTLS Deployment Patterns . . . . . . . . . . . . . . . . 121
12.16. Interception of Responses from the AS . . . . . . . . . 121
12.17. Key Distribution . . . . . . . . . . . . . . . . . . . . 122
12.18. Interaction Finish Modes and Polling . . . . . . . . . . 122
12.19. Storage of Information During Interaction and
Continuation . . . . . . . . . . . . . . . . . . . . . 123
12.20. Denial of Service (DoS) through Grant Continuation . . . 124
12.21. Exhaustion of Random Value Space . . . . . . . . . . . . 124
13. Privacy Considerations . . . . . . . . . . . . . . . . . . . 125
13.1. Surveillance . . . . . . . . . . . . . . . . . . . . . . 125
13.1.1. Surveillance by the Client . . . . . . . . . . . . . 125
13.1.2. Surveillance by the Authorization Server . . . . . . 125
13.2. Stored Data . . . . . . . . . . . . . . . . . . . . . . 126
13.3. Intrusion . . . . . . . . . . . . . . . . . . . . . . . 127
13.4. Correlation . . . . . . . . . . . . . . . . . . . . . . 127
13.4.1. Correlation by Clients . . . . . . . . . . . . . . . 127
13.4.2. Correlation by Resource Servers . . . . . . . . . . 127
13.4.3. Correlation by Authorization Servers . . . . . . . . 128
13.5. Disclosure in Shared References . . . . . . . . . . . . 128
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 128
14.1. Normative References . . . . . . . . . . . . . . . . . . 128
14.2. Informative References . . . . . . . . . . . . . . . . . 131
Appendix A. Document History . . . . . . . . . . . . . . . . . . 131
Appendix B. Compared to OAuth 2.0 . . . . . . . . . . . . . . . 134
Appendix C. Component Data Models . . . . . . . . . . . . . . . 136
Appendix D. Example Protocol Flows . . . . . . . . . . . . . . . 136
D.1. Redirect-Based User Interaction . . . . . . . . . . . . . 137
D.2. Secondary Device Interaction . . . . . . . . . . . . . . 140
D.3. No User Involvement . . . . . . . . . . . . . . . . . . . 143
D.4. Asynchronous Authorization . . . . . . . . . . . . . . . 144
D.5. Applying OAuth 2.0 Scopes and Client IDs . . . . . . . . 148
Appendix E. JSON Structures and Polymorphism . . . . . . . . . . 149
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 150
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1. Introduction
This protocol allows a piece of software, the client instance, to
request delegated authorization to resource servers and to request
direct information. This delegation is facilitated by an
authorization server usually on behalf of a resource owner. The end-
user operating the software may interact with the authorization
server to authenticate, provide consent, and authorize the request.
The process by which the delegation happens is known as a grant, and
GNAP allows for the negotiation of the grant process over time by
multiple parties acting in distinct roles.
This specification focuses on the portions of the delegation process
facing the client instance. In particular, this specification
defines interoperable methods for a client instance to request,
negotiate, and receive access to information facilitated by the
authorization server. This specification also discusses discovery
mechanisms for the client instance to configure itself dynamically.
The means for an authorization server and resource server to
interoperate are discussed in the companion document,
[I-D.draft-ietf-gnap-resource-servers].
The focus of this protocol is to provide interoperability between the
different parties acting in each role, and is not to specify
implementation details of each. Where appropriate, GNAP may make
recommendations about internal implementation details, but these
recommendations are to ensure the security of the overall deployment
rather than to be prescriptive in the implementation.
This protocol solves many of the same use cases as OAuth 2.0
[RFC6749], OpenID Connect [OIDC], and the family of protocols that
have grown up around that ecosystem. However, GNAP is not an
extension of OAuth 2.0 and is not intended to be directly compatible
with OAuth 2.0. GNAP seeks to provide functionality and solve use
cases that OAuth 2.0 cannot easily or cleanly address. Appendix B
further details the protocol rationale compared to OAuth 2.0. GNAP
and OAuth 2.0 will likely exist in parallel for many deployments, and
considerations have been taken to facilitate the mapping and
transition from legacy systems to GNAP. Some examples of these can
be found in Appendix D.5.
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1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document contains non-normative examples of partial and complete
HTTP messages, JSON structures, URLs, query components, keys, and
other elements. Some examples use a single trailing backslash '' to
indicate line wrapping for long values, as per [RFC8792]. The "\"
character and leading spaces on wrapped lines are not part of the
value.
1.2. Roles
The parties in GNAP perform actions under different roles. Roles are
defined by the actions taken and the expectations leveraged on the
role by the overall protocol.
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+-------------+ +------------+
| | | |
|Authorization| | Resource |
| Server | | Server |
| |<-+ +---->| |
+-------------+ | | +------------+
+ | |
+ | |
+ | |
+ | |
+ | |
+ +----------+
+ | Client |
+ | Instance |
+ +----------+
+ +
+ +
+ +
+-----------+ + +------------+
| | + + + +| |
| Resource | | End |
| Owner | ~ ~ ~ ~ ~ ~ | User |
| | | |
+-----------+ +------------+
Legend
+ + + indicates interaction between a human and computer
----- indicates interaction between two pieces of software
~ ~ ~ indicates a potential equivalence or out-of-band
communication between roles
Authorization Server (AS) server that grants delegated privileges to
a particular instance of client software in the form of access
tokens or other information (such as subject information).
Client application operated by an end-user that consumes resources
from one or several RSs, possibly requiring access privileges from
one or several ASs. Example: a client can be a mobile
application, a web application, etc. Note: this specification
differentiates between a specific instance (the client instance,
identified by its unique key) and the software running the
instance (the client software). For some kinds of client
software, there could be many instances of that software, each
instance with a different key.
Resource Server (RS) server that provides operations on protected
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resources, where operations require a valid access token issued by
an AS.
Resource Owner (RO) subject entity that may grant or deny operations
on resources it has authority upon. Note: the act of granting or
denying an operation may be manual (i.e. through an interaction
with a physical person) or automatic (i.e. through predefined
organizational rules).
End-user natural person that operates a client instance. Note: that
natural person may or may not be the same entity as the RO.
The design of GNAP does not assume any one deployment architecture,
but instead attempts to define roles that can be fulfilled in a
number of different ways for different use cases. As long as a given
role fulfills all of its obligations and behaviors as defined by the
protocol, GNAP does not make additional requirements on its structure
or setup.
Multiple roles can be fulfilled by the same party, and a given party
can switch roles in different instances of the protocol. For
example, the RO and end-user in many instances are the same person,
where a user is authorizing the client instance to act on their own
behalf at the RS. In this case, one party fulfills both of the RO
and end-user roles, but the roles themselves are still defined
separately from each other to allow for other use cases where they
are fulfilled by different parties.
For another example, in some complex scenarios, an RS receiving
requests from one client instance can act as a client instance for a
downstream secondary RS in order to fulfill the original request. In
this case, one piece of software is both an RS and a client instance
from different perspectives, and it fulfills these roles separately
as far as the overall protocol is concerned.
A single role need not be deployed as a monolithic service. For
example, A client instance could have components that are installed
on the end-user's device as well as a back-end system that it
communicates with. If both of these components participate in the
delegation protocol, they are both considered part of the client
instance. If there are several copies of the client software that
run separately but all share the same key material, such as a
deployed cluster, then this cluster is considered a single client
instance.
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In these cases, the distinct components of what is considered a GNAP
client instance may use any number of different communication
mechanisms between them, all of which would be considered an
implementation detail of the client instances and out of scope of
GNAP.
For another example, an AS could likewise be built out of many
constituent components in a distributed architecture. The component
that the client instance calls directly could be different from the
component that the RO interacts with to drive consent, since API
calls and user interaction have different security considerations in
many environments. Furthermore, the AS could need to collect
identity claims about the RO from one system that deals with user
attributes while generating access tokens at another system that
deals with security rights. From the perspective of GNAP, all of
these are pieces of the AS and together fulfill the role of the AS as
defined by the protocol. These pieces may have their own internal
communications mechanisms which are considered out of scope of GNAP.
1.3. Elements
In addition to the roles above, the protocol also involves several
elements that are acted upon by the roles throughout the process.
Attribute characteristics related to a subject.
Access Token a data artifact representing a set of rights and/or
attributes. Note: an access token can be first issued to an
client instance (requiring authorization by the RO) and
subsequently rotated.
Grant (verb): to permit an instance of client software to receive
some attributes at a specific time and valid for a specific
duration and/or to exercise some set of delegated rights to access
a protected resource (noun): the act of granting.
Privilege right or attribute associated with a subject. Note: the
RO defines and maintains the rights and attributes associated to
the protected resource, and might temporarily delegate some set of
those privileges to an end-user. This process is refered to as
privilege delegation.
Protected Resource protected API (Application Programming Interface)
served by an RS and that can be accessed by a client, if and only
if a valid access token is provided. Note: to avoid complex
sentences, the specification document may simply refer to resource
instead of protected resource.
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Right ability given to a subject to perform a given operation on a
resource under the control of an RS.
Subject person, organization or device.
Subject Information statement asserted by an AS about a subject.
1.4. Trust relationships
GNAP defines its trust objective as: "the RO trusts the AS to ensure
access validation and delegation of protected resources to end-users,
through third party clients."
This trust objective can be decomposed into trust relationships
between software elements and roles, especially the pairs end-user/
RO, end-user/client, client/AS, RS/RO, AS/RO, AS/RS. Trust of an
agent by its pair can exist if the pair is informed that the agent
has made a promise to follow the protocol in the past (e.g. pre-
registration, uncompromised cryptographic components) or if the pair
is able to infer by indirect means that the agent has made such a
promise (e.g. a compliant client request). Each agent defines its
own valuation function of promises given or received. Examples of
such valuations can be the benefits from interacting with other
agents (e.g. safety in client access, interoperability with identity
standards), the cost of following the protocol (including its
security and privacy requirements and recommendations), a ranking of
promise importance (e.g. a policy decision made by the AS), the
assessment of one's vulnerability or risk of not being able to defend
against threats, etc. Those valuations may depend on the context of
the request. For instance, the AS may decide to either take into
account or discard hints provided by the client, the RS may refuse
bearer tokens, etc. depending on the specific case in which GNAP is
used. Some promises can be conditional of some previous interactions
(e.g. repeated requests).
Looking back on each trust relationship:
* end-user/RO: this relationship exists only when the end-user and
the RO are different, in which case the end-user needs some out of
band mechanism of getting the RO consent (see Section 4). GNAP
generally assumes that humans can be authenticated thanks to
identity protocols (for instance, through an id_token assertion in
Section 2.2).
* end-user/client: the client acts as a user agent. Depending on
the technology used (browser, SPA, mobile application, IoT device,
etc.), some interactions may or may not be possible (as described
in Section 2.5.1). Client developers promise to implement
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requirements and generally some recommendations or best practices,
so that the end-users may confidently use their software.
However, end-users might also be facing some attacker's client
software, without even realizing it.
* client/AS: An honest AS may be facing an attacker's client (as
discussed just above), or the reverse, and GNAP aims at making
common attacks impractical. The core specification makes access
tokens opaque to the client and defines the request/response
scheme in detail, therefore avoiding extra trust hypotheses from
this critical piece of software. Yet the AS may further define
cryptographic attestations or optional rules to simplify the
access of clients it already trusts, due to past behavior or
organizational policies (see Section 2.3).
* RS/RO: the RS promises it protects its resources from unauthorized
access, and only accepts valid access tokens issued by a trusted
AS. In case tokens are key bound, proper validation is expected
from the RS.
* AS/RO: the AS is expected to follow the decisions made by the RO,
either through interactive consent requests, repeated interactions
or automated rules (as described in Section 1.5). Privacy
considerations aim to reduce the risk of an honest but too curious
AS, or the consequences of an unexpected user data exposure.
* AS/RS: the AS promises to issue valid access tokens to legitimate
client requests (i.e. after carrying out appropriate due
diligence, as defined in the GNAP protocol). Some optional
configurations are covered by
[I-D.draft-ietf-gnap-resource-servers].
A global assumption made by GNAP is that authorization requests are
security and privacy sensitive, and appropriate measures are
respectively detailed in Section 12 and Section 13.
A formal trust model is out of scope of this specification, but might
be carried out thanks to [promise-theory].
1.5. Sequences
GNAP can be used in a variety of ways to allow the core delegation
process to take place. Many portions of this process are
conditionally present depending on the context of the deployments,
and not every step in this overview will happen in all circumstances.
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Note that a connection between roles in this process does not
necessarily indicate that a specific protocol message is sent across
the wire between the components fulfilling the roles in question, or
that a particular step is required every time. For example, for a
client instance interested in only getting subject information
directly, and not calling an RS, all steps involving the RS below do
not apply.
In some circumstances, the information needed at a given stage is
communicated out of band or is preconfigured between the components
or entities performing the roles. For example, one entity can fulfil
multiple roles, and so explicit communication between the roles is
not necessary within the protocol flow. Additionally some components
may not be involved in all use cases. For example, a client instance
could be calling the AS just to get direct user information and have
no need to get an access token to call an RS.
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+------------+ +------------+
| End-user | ~ ~ ~ ~ | Resource |
| | | Owner (RO) |
+------------+ +------------+
+ +
+ +
(A) (B)
+ +
+ +
+--------+ + +------------+
| Client | (1) + | Resource |
|Instance| + | Server |
| | +---------------+ | (RS) |
| |--(2)->| Authorization | | |
| |<-(3)--| Server | | |
| | | (AS) | | |
| |--(4)->| | | |
| |<-(5)--| | | |
| |--------------(6)------------->| |
| | | | (7) | |
| |<-------------(8)------------->| |
| |--(9)->| | | |
| |<-(10)-| | | |
| |--------------(11)------------>| |
| | | | (12) | |
| |-(13)->| | | |
| | | | | |
+--------+ +---------------+ +------------+
Legend
+ + + indicates a possible interaction with a human
----- indicates an interaction between protocol roles
~ ~ ~ indicates a potential equivalence or out-of-band
communication between roles
* (A) The end-user interacts with the client instance to indicate a
need for resources on behalf of the RO. This could identify the
RS the client instance needs to call, the resources needed, or the
RO that is needed to approve the request. Note that the RO and
end-user are often the same entity in practice, but some more
dynamic processes are discussed in
[I-D.draft-ietf-gnap-resource-servers].
* (1) The client instance determines what access is needed and which
AS to approach for access. Note that for most situations, the
client instance is pre-configured with which AS to talk to and
which kinds of access it needs.
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* (2) The client instance requests access at the AS (Section 2).
* (3) The AS processes the request and determines what is needed to
fulfill the request. The AS sends its response to the client
instance (Section 3).
* (B) If interaction is required, the AS interacts with the RO
(Section 4) to gather authorization. The interactive component of
the AS can function using a variety of possible mechanisms
including web page redirects, applications, challenge/response
protocols, or other methods. The RO approves the request for the
client instance being operated by the end-user. Note that the RO
and end-user are often the same entity in practice.
* (4) The client instance continues the grant at the AS (Section 5).
* (5) If the AS determines that access can be granted, it returns a
response to the client instance (Section 3) including an access
token (Section 3.2) for calling the RS and any directly returned
information (Section 3.4) about the RO.
* (6) The client instance uses the access token (Section 7.2) to
call the RS.
* (7) The RS determines if the token is sufficient for the request
by examining the token. The means of the RS determining this
access are out of scope of this specification, but some options
are discussed in [I-D.draft-ietf-gnap-resource-servers].
* (8) The client instance calls the RS (Section 7.2) using the
access token until the RS or client instance determine that the
token is no longer valid.
* (9) When the token no longer works, the client instance fetches an
updated access token (Section 6.1) based on the rights granted in
(5).
* (10) The AS issues a new access token (Section 3.2) to the client
instance.
* (11) The client instance uses the new access token (Section 7.2)
to call the RS.
* (12) The RS determines if the new token is sufficient for the
request. The means of the RS determining this access are out of
scope of this specification, but some options are discussed in
[I-D.draft-ietf-gnap-resource-servers].
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* (13) The client instance disposes of the token (Section 6.2) once
the client instance has completed its access of the RS and no
longer needs the token.
The following sections and Appendix D contain specific guidance on
how to use GNAP in different situations and deployments. For
example, it is possible for the client instance to never request an
access token and never call an RS, just as it is possible for there
not to be a user involved in the delegation process.
1.5.1. Redirect-based Interaction
In this example flow, the client instance is a web application that
wants access to resources on behalf of the current user, who acts as
both the end-user and the resource owner (RO). Since the client
instance is capable of directing the user to an arbitrary URL and
receiving responses from the user's browser, interaction here is
handled through front-channel redirects using the user's browser.
The redirection URL used for interaction is a service hosted by the
AS in this example. The client instance uses a persistent session
with the user to ensure the same user that is starting the
interaction is the user that returns from the interaction.
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+--------+ +--------+ +------+
| Client | | AS | | User |
|Instance| | | | |
| |< (1) + Start Session + + + + + + + + + + + + + + + +| |
| | | | | |
| |--(2)--- Request Access --------->| | | |
| | | | | |
| |<-(3)-- Interaction Needed -------| | | |
| | | | | |
| |+ (4) + Redirect for Interaction + + + + + + + + + > | |
| | | | | |
| | | |<+ (5) +>| |
| | | | AuthN | |
| | | | | |
| | | |<+ (6) +>| |
| | | | AuthZ | |
| | | | | |
| |< (7) + Redirect for Continuation + + + + + + + + + +| |
| | | | +------+
| |--(8)--- Continue Request ------->| |
| | | |
| |<-(9)----- Grant Access ----------| |
| | | |
| | | | +--------+
| |--(10)-- Access API ---------------------------->| RS |
| | | | | |
| |<-(11)-- API Response ---------------------------| |
| | | | +--------+
+--------+ +--------+
1. The client instance establishes a verifiable session to the
user, in the role of the end-user.
2. The client instance requests access to the resource (Section 2).
The client instance indicates that it can redirect to an
arbitrary URL (Section 2.5.1.1) and receive a redirect from the
browser (Section 2.5.2.1). The client instance stores
verification information for its redirect in the session created
in (1).
3. The AS determines that interaction is needed and responds
(Section 3) with a URL to send the user to (Section 3.3.1) and
information needed to verify the redirect (Section 3.3.4) in
(7). The AS also includes information the client instance will
need to continue the request (Section 3.1) in (8). The AS
associates this continuation information with an ongoing request
that will be referenced in (4), (6), and (8).
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4. The client instance stores the verification and continuation
information from (3) in the session from (1). The client
instance then redirects the user to the URL (Section 4.1.1)
given by the AS in (3). The user's browser loads the
interaction redirect URL. The AS loads the pending request
based on the incoming URL generated in (3).
5. The user authenticates at the AS, taking on the role of the RO.
6. As the RO, the user authorizes the pending request from the
client instance.
7. When the AS is done interacting with the user, the AS redirects
the user back (Section 4.2.1) to the client instance using the
redirect URL provided in (2). The redirect URL is augmented
with an interaction reference that the AS associates with the
ongoing request created in (2) and referenced in (4). The
redirect URL is also augmented with a hash of the security
information provided in (2) and (3). The client instance loads
the verification information from (2) and (3) from the session
created in (1). The client instance calculates a hash
(Section 4.2.3) based on this information and continues only if
the hash validates. Note that the client instance needs to
ensure that the parameters for the incoming request match those
that it is expecting from the session created in (1). The
client instance also needs to be prepared for the end-user never
being returned to the client instance and handle timeouts
appropriately.
8. The client instance loads the continuation information from (3)
and sends the interaction reference from (7) in a request to
continue the request (Section 5.1). The AS validates the
interaction reference ensuring that the reference is associated
with the request being continued.
9. If the request has been authorized, the AS grants access to the
information in the form of access tokens (Section 3.2) and
direct subject information (Section 3.4) to the client instance.
10. The client instance uses the access token (Section 7.2) to call
the RS.
11. The RS validates the access token and returns an appropriate
response for the API.
An example set of protocol messages for this method can be found in
Appendix D.1.
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1.5.2. User-code Interaction
In this example flow, the client instance is a device that is capable
of presenting a short, human-readable code to the user and directing
the user to enter that code at a known URL. The URL the user enters
the code at is an interactive service hosted by the AS in this
example. The client instance is not capable of presenting an
arbitrary URL to the user, nor is it capable of accepting incoming
HTTP requests from the user's browser. The client instance polls the
AS while it is waiting for the RO to authorize the request. The
user's interaction is assumed to occur on a secondary device. In
this example it is assumed that the user is both the end-user and RO,
though the user is not assumed to be interacting with the client
instance through the same web browser used for interaction at the AS.
+--------+ +--------+ +------+
| Client | | AS | | User |
|Instance|--(1)--- Request Access --------->| | | |
| | | | | |
| |<-(2)-- Interaction Needed -------| | | |
| | | | | |
| |+ (3) + + Display User Code + + + + + + + + + + + + >| |
| | | | | |
| | | |<+ (4) + | |
| | | |Open URI | |
| | | | | |
| | | |<+ (5) +>| |
| | | | AuthN | |
| |--(9)--- Continue Request (A) --->| | | |
| | | |<+ (6) +>| |
| |<-(10)- Not Yet Granted (Wait) ---| | Code | |
| | | | | |
| | | |<+ (7) +>| |
| | | | AuthZ | |
| | | | | |
| | | |<+ (8) +>| |
| | | |Completed| |
| | | | | |
| |--(11)-- Continue Request (B) --->| | +------+
| | | |
| |<-(12)----- Grant Access ---------| |
| | | |
| | | | +--------+
| |--(13)-- Access API ---------------------------->| RS |
| | | | | |
| |<-(14)-- API Response ---------------------------| |
| | | | +--------+
+--------+ +--------+
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1. The client instance requests access to the resource (Section 2).
The client instance indicates that it can display a user code
(Section 2.5.1.3).
2. The AS determines that interaction is needed and responds
(Section 3) with a user code to communicate to the user
(Section 3.3.3). This could optionally include a URL to direct
the user to, but this URL should be static and so could be
configured in the client instance's documentation. The AS also
includes information the client instance will need to continue
the request (Section 3.1) in (8) and (10). The AS associates
this continuation information with an ongoing request that will
be referenced in (4), (6), (8), and (10).
3. The client instance stores the continuation information from (2)
for use in (8) and (10). The client instance then communicates
the code to the user (Section 4.1.1) given by the AS in (2).
4. The user's directs their browser to the user code URL. This URL
is stable and can be communicated via the client software's
documentation, the AS documentation, or the client software
itself. Since it is assumed that the RO will interact with the
AS through a secondary device, the client instance does not
provide a mechanism to launch the RO's browser at this URL.
5. The end-user authenticates at the AS, taking on the role of the
RO.
6. The RO enters the code communicated in (3) to the AS. The AS
validates this code against a current request in process.
7. As the RO, the user authorizes the pending request from the
client instance.
8. When the AS is done interacting with the user, the AS indicates
to the RO that the request has been completed.
9. Meanwhile, the client instance loads the continuation
information stored at (3) and continues the request (Section 5).
The AS determines which ongoing access request is referenced
here and checks its state.
10. If the access request has not yet been authorized by the RO in
(6), the AS responds to the client instance to continue the
request (Section 3.1) at a future time through additional polled
continuation requests. This response can include updated
continuation information as well as information regarding how
long the client instance should wait before calling again. The
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client instance replaces its stored continuation information
from the previous response (2). Note that the AS may need to
determine that the RO has not approved the request in a
sufficient amount of time and return an appropriate error to the
client instance.
11. The client instance continues to poll the AS (Section 5.2) with
the new continuation information in (9).
12. If the request has been authorized, the AS grants access to the
information in the form of access tokens (Section 3.2) and
direct subject information (Section 3.4) to the client instance.
13. The client instance uses the access token (Section 7.2) to call
the RS.
14. The RS validates the access token and returns an appropriate
response for the API.
An example set of protocol messages for this method can be found in
Appendix D.2.
1.5.3. Asynchronous Authorization
In this example flow, the end-user and RO roles are fulfilled by
different parties, and the RO does not interact with the client
instance. The AS reaches out asynchronously to the RO during the
request process to gather the RO's authorization for the client
instance's request. The client instance polls the AS while it is
waiting for the RO to authorize the request.
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+--------+ +--------+ +------+
| Client | | AS | | RO |
|Instance|--(1)--- Request Access --------->| | | |
| | | | | |
| |<-(2)-- Not Yet Granted (Wait) ---| | | |
| | | |<+ (3) +>| |
| | | | AuthN | |
| |--(6)--- Continue Request (A) --->| | | |
| | | |<+ (4) +>| |
| |<-(7)-- Not Yet Granted (Wait) ---| | AuthZ | |
| | | | | |
| | | |<+ (5) +>| |
| | | |Completed| |
| | | | | |
| |--(8)--- Continue Request (B) --->| | +------+
| | | |
| |<-(9)------ Grant Access ---------| |
| | | |
| | | | +--------+
| |--(10)-- Access API ---------------------------->| RS |
| | | | | |
| |<-(11)-- API Response ---------------------------| |
| | | | +--------+
+--------+ +--------+
1. The client instance requests access to the resource (Section 2).
The client instance does not send any interactions modes to the
server, indicating that it does not expect to interact with the
RO. The client instance can also signal which RO it requires
authorization from, if known, by using the user request section
(Section 2.4).
2. The AS determines that interaction is needed, but the client
instance cannot interact with the RO. The AS responds
(Section 3) with the information the client instance will need
to continue the request (Section 3.1) in (6) and (8), including
a signal that the client instance should wait before checking
the status of the request again. The AS associates this
continuation information with an ongoing request that will be
referenced in (3), (4), (5), (6), and (8).
3. The AS determines which RO to contact based on the request in
(1), through a combination of the user request (Section 2.4),
the resources request (Section 2.1), and other policy
information. The AS contacts the RO and authenticates them.
4. The RO authorizes the pending request from the client instance.
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5. When the AS is done interacting with the RO, the AS indicates to
the RO that the request has been completed.
6. Meanwhile, the client instance loads the continuation
information stored at (2) and continues the request (Section 5).
The AS determines which ongoing access request is referenced
here and checks its state.
7. If the access request has not yet been authorized by the RO in
(6), the AS responds to the client instance to continue the
request (Section 3.1) at a future time through additional
polling. This response can include refreshed credentials as
well as information regarding how long the client instance
should wait before calling again. The client instance replaces
its stored continuation information from the previous response
(2). Note that the AS may need to determine that the RO has not
approved the request in a sufficient amount of time and return
an appropriate error to the client instance.
8. The client instance continues to poll the AS (Section 5.2) with
the new continuation information from (7).
9. If the request has been authorized, the AS grants access to the
information in the form of access tokens (Section 3.2) and
direct subject information (Section 3.4) to the client instance.
10. The client instance uses the access token (Section 7.2) to call
the RS.
11. The RS validates the access token and returns an appropriate
response for the API.
An example set of protocol messages for this method can be found in
Appendix D.4.
1.5.4. Software-only Authorization
In this example flow, the AS policy allows the client instance to
make a call on its own behalf, without the need for a RO to be
involved at runtime to approve the decision. Since there is no
explicit RO, the client instance does not interact with an RO.
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+--------+ +--------+
| Client | | AS |
|Instance|--(1)--- Request Access --->| |
| | | |
| |<-(2)---- Grant Access -----| |
| | | | +--------+
| |--(3)--- Access API ------------------->| RS |
| | | | | |
| |<-(4)--- API Response ------------------| |
| | | | +--------+
+--------+ +--------+
1. The client instance requests access to the resource (Section 2).
The client instance does not send any interactions modes to the
server.
2. The AS determines that the request is been authorized, the AS
grants access to the information in the form of access tokens
(Section 3.2) to the client instance. Note that direct subject
information (Section 3.4) is not generally applicable in this use
case, as there is no user involved.
3. The client instance uses the access token (Section 7.2) to call
the RS.
4. The RS validates the access token and returns an appropriate
response for the API.
An example set of protocol messages for this method can be found in
Appendix D.3.
1.5.5. Refreshing an Expired Access Token
In this example flow, the client instance receives an access token to
access a resource server through some valid GNAP process. The client
instance uses that token at the RS for some time, but eventually the
access token expires. The client instance then gets a new access
token by rotating the expired access token at the AS using the
token's management URL.
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+--------+ +--------+
| Client | | AS |
|Instance|--(1)--- Request Access ----------------->| |
| | | |
| |<-(2)--- Grant Access --------------------| |
| | | |
| | +--------+ | |
| |--(3)--- Access Resource --->| RS | | |
| | | | | |
| |<-(4)--- Success Response ---| | | |
| | | | | |
| | | | | |
| | | | | |
| |--(5)--- Access Resource --->| | | |
| | | | | |
| |<-(6)--- Error Response -----| | | |
| | +--------+ | |
| | | |
| |--(7)--- Rotate Token ------------------->| |
| | | |
| |<-(8)--- Rotated Token -------------------| |
| | | |
+--------+ +--------+
1. The client instance requests access to the resource (Section 2).
2. The AS grants access to the resource (Section 3) with an access
token (Section 3.2) usable at the RS. The access token response
includes a token management URI.
3. The client instance uses the access token (Section 7.2) to call
the RS.
4. The RS validates the access token and returns an appropriate
response for the API.
5. Time passes and the client instance uses the access token to call
the RS again.
6. The RS validates the access token and determines that the access
token is expired The RS responds to the client instance with an
error.
7. The client instance calls the token management URI returned in
(2) to rotate the access token (Section 6.1). The client
instance uses the access token (Section 7.2) in this call as well
as the appropriate key, see the token rotation section for
details.
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8. The AS validates the rotation request including the signature and
keys presented in (5) and returns a new access token
(Section 3.2.1). The response includes a new access token and
can also include updated token management information, which the
client instance will store in place of the values returned in
(2).
1.5.6. Requesting User Information
In this scenario, the client instance does not call an RS and does
not request an access token. Instead, the client instance only
requests and is returned direct subject information (Section 3.4).
Many different interaction modes can be used in this scenario, so
these are shown only in the abstract as functions of the AS here.
+--------+ +--------+ +------+
| Client | | AS | | User |
|Instance| | | | |
| |--(1)--- Request Access --------->| | | |
| | | | | |
| |<-(2)--- Request Access ----------| | | |
| | | | | |
| |+ (3) + Facilitate Interaction + + + + + + + + + + > | |
| | | | | |
| | | |<+ (4) +>| |
| | | | AuthN | |
| | | | | |
| | | |<+ (5) +>| |
| | | | AuthZ | |
| | | | | |
| |< (6) + Signal Continuation + + + + + + + + + + + + +| |
| | | | +------+
| |--(7)--- Continue Request ------->| |
| | | |
| |<-(8)----- Grant Access ----------| |
| | | |
+--------+ +--------+
1. The client instance requests access to subject information
(Section 2).
2. The AS determines that interaction is needed and responds
(Section 3) with appropriate information for facilitating user
interaction (Section 3.3).
3. The client instance facilitates the user interacting with the AS
(Section 4) as directed in (2).
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4. The user authenticates at the AS, taking on the role of the RO.
5. As the RO, the user authorizes the pending request from the
client instance.
6. When the AS is done interacting with the user, the AS returns the
user to the client instance and signals continuation.
7. The client instance loads the continuation information from (2)
and calls the AS to continue the request (Section 5).
8. If the request has been authorized, the AS grants access to the
requested direct subject information (Section 3.4) to the client
instance. At this stage, the user is generally considered
"logged in" to the client instance based on the identifiers and
assertions provided by the AS. Note that the AS can restrict the
subject information returned and it might not match what the
client instance requested, see the section on subject information
for details.
2. Requesting Access
To start a request, the client instance sends JSON [RFC8259] document
with an object as its root. Each member of the request object
represents a different aspect of the client instance's request. Each
field is described in detail in a section below.
access_token (object / array of objects) Describes the rights and
properties associated with the requested access token.
Section 2.1
subject (object) Describes the information about the RO that the
client instance is requesting to be returned directly in the
response from the AS. Section 2.2
client (object / string) Describes the client instance that is
making this request, including the key that the client instance
will use to protect this request and any continuation requests at
the AS and any user-facing information about the client instance
used in interactions. Section 2.3
user (object / string) Identifies the end-user to the AS in a manner
that the AS can verify, either directly or by interacting with the
end-user to determine their status as the RO. Section 2.4
interact (object) Describes the modes that the client instance has
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for allowing the RO to interact with the AS and modes for the
client instance to receive updates when interaction is complete.
Section 2.5
Additional members of this request object can be defined by
extensions to this protocol as described in Section 2.6
A non-normative example of a grant request is below:
{
"access_token": {
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"dolphin-metadata"
]
},
"client": {
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
},
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeL...."
}
}
},
"interact": {
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"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
},
"subject": {
"formats": ["iss_sub", "opaque"],
"assertions": ["id_token"]
}
}
The request and response MUST be sent as a JSON object in the body of
the HTTP POST request with Content-Type "application/json", unless
otherwise specified by the signature mechanism.
The authorization server MUST include the HTTP "Cache-Control"
response header field [RFC7234] with a value set to "no-store".
2.1. Requesting Access to Resources
If the client instance is requesting one or more access tokens for
the purpose of accessing an API, the client instance MUST include an
"access_token" field. This field MUST be an object (for a single
access token (Section 2.1.1)) or an array of these objects (for
multiple access tokens (Section 2.1.2)), as described in the
following sections.
2.1.1. Requesting a Single Access Token
To request a single access token, the client instance sends an
"acccess_token" object composed of the following fields.
access (array of objects/strings) Describes the rights that the
client instance is requesting for one or more access tokens to be
used at RS's. This field is REQUIRED. Section 8
label (string) A unique name chosen by the client instance to refer
to the resulting access token. The value of this field is opaque
to the AS. If this field is included in the request, the AS MUST
include the same label in the token response (Section 3.2). This
field is REQUIRED if used as part of a multiple access token
request (Section 2.1.2), and is OPTIONAL otherwise.
flags (array of strings) A set of flags that indicate desired
attributes or behavior to be attached to the access token by the
AS. This field is OPTIONAL.
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The values of the "flags" field defined by this specification are as
follows:
"bearer" If this flag is included, the access token being requested
is a bearer token. If this flag is omitted, the access token is
bound to the key used by the client instance in this request, or
the key's most recent rotation. Methods for presenting bound and
bearer access tokens are described in Section 7.2. [[ See issue
#38 (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/38)
]]
"split" If this flag is included, the client instance is capable of
receiving a different number of tokens than specified in the token
request (Section 2.1), including receiving multiple access tokens
(Section 3.2.2) in response to any single token request
(Section 2.1.1) or a different number of access tokens than
requested in a multiple access token request (Section 2.1.2). The
"label" fields of the returned additional tokens are chosen by the
AS. The client instance MUST be able to tell from the token
response where and how it can use each of the access tokens. [[
See issue #37 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/37) ]]
Flag values MUST NOT be included more than once.
Additional flags can be defined by extensions using a registry TBD
(Section 11).
In the following example, the client instance is requesting access to
a complex resource described by a pair of access request object.
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"access_token": {
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"delete"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
{
"type": "walrus-access",
"actions": [
"foo",
"bar"
],
"locations": [
"https://resource.other/"
],
"datatypes": [
"data",
"pictures",
"walrus whiskers"
]
}
],
"label": "token1-23",
"flags": [ "split" ]
}
If access is approved, the resulting access token is valid for the
described resource and is bound to the client instance's key (or its
most recent rotation). The token is labeled "token1-23" and could be
split into multiple access tokens by the AS, if the AS chooses. The
token response structure is described in Section 3.2.1.
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2.1.2. Requesting Multiple Access Tokens
To request multiple access tokens to be returned in a single
response, the client instance sends an array of objects as the value
of the "access_token" parameter. Each object MUST conform to the
request format for a single access token request, as specified in
requesting a single access token (Section 2.1.1). Additionally, each
object in the array MUST include the "label" field, and all values of
these fields MUST be unique within the request. If the client
instance does not include a "label" value for any entry in the array,
or the values of the "label" field are not unique within the array,
the AS MUST return an error.
The following non-normative example shows a request for two separate
access tokens, "token1" and "token2".
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"access_token": [
{
"label": "token1",
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"dolphin-metadata"
]
},
{
"label": "token2",
"access": [
{
"type": "walrus-access",
"actions": [
"foo",
"bar"
],
"locations": [
"https://resource.other/"
],
"datatypes": [
"data",
"pictures",
"walrus whiskers"
]
}
],
"flags": [ "bearer" ]
}
]
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All approved access requests are returned in the multiple access
token response (Section 3.2.2) structure using the values of the
"label" fields in the request.
2.2. Requesting Subject Information
If the client instance is requesting information about the RO from
the AS, it sends a "subject" field as a JSON object. This object MAY
contain the following fields (or additional fields defined in a
registry TBD (Section 11)).
formats (array of strings) An array of subject identifier subject
types requested for the RO, as defined by
[I-D.ietf-secevent-subject-identifiers].
assertions (array of strings) An array of requested assertion
formats. Possible values include "id_token" for an [OIDC] ID
Token and "saml2" for a SAML 2 assertion. Additional assertion
values are defined by a registry TBD (Section 11). [[ See issue
#41 (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/41)
]]
"subject": {
"formats": [ "iss_sub", "opaque" ],
"assertions": [ "id_token", "saml2" ]
}
The AS can determine the RO's identity and permission for releasing
this information through interaction with the RO (Section 4), AS
policies, or assertions presented by the client instance
(Section 2.4). If this is determined positively, the AS MAY return
the RO's information in its response (Section 3.4) as requested.
Subject identifier types requested by the client instance serve only
to identify the RO in the context of the AS and can't be used as
communication channels by the client instance, as discussed in
Section 3.4.
The AS SHOULD NOT re-use subject identifiers for multiple different
ROs.
Note: the "formats" and "assertions" request fields are independent
of each other, and a returned assertion MAY omit a requested subject
identifier.
[[ See issue #43 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/43) ]]
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2.3. Identifying the Client Instance
When sending a non-continuation request to the AS, the client
instance MUST identify itself by including the "client" field of the
request and by signing the request as described in Section 7.3. Note
that for a continuation request (Section 5), the client instance is
identified by its association with the request being continued and so
this field is not sent under those circumstances.
When client instance information is sent by value, the "client" field
of the request consists of a JSON object with the following fields.
key (object / string) The public key of the client instance to be
used in this request as described in Section 7.1 or a reference to
a key as described in Section 7.1.1. This field is REQUIRED.
class_id (string) An identifier string that the AS can use to
identify the client software comprising this client instance. The
contents and format of this field are up to the AS. This field is
OPTIONAL.
display (object) An object containing additional information that
the AS MAY display to the RO during interaction, authorization,
and management. This field is OPTIONAL.
"client": {
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8..."
},
"cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFA..."
},
"class_id": "web-server-1234",
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
}
}
Additional fields are defined in a registry TBD (Section 11).
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The client instance MUST prove possession of any presented key by the
"proof" mechanism associated with the key in the request. Proof
types are defined in a registry TBD (Section 11) and an initial set
of methods is described in Section 7.3.
Note that the AS MAY know the client instance's public key ahead of
time, and the AS MAY apply different policies to the request
depending on what has been registered against that key. If the same
public key is sent by value on subsequent access requests, the AS
SHOULD treat these requests as coming from the same client instance
for purposes of identification, authentication, and policy
application. If the AS does not know the client instance's public
key ahead of time, the AS MAY accept or reject the request based on
AS policy, attestations within the "client" request, and other
mechanisms.
[[ See issue #44 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/44) ]]
2.3.1. Identifying the Client Instance by Reference
If the client instance has an instance identifier that the AS can use
to determine appropriate key information, the client instance can
send this instance identifier as a direct reference value in lieu of
the "client" object. The instance identifier MAY be assigned to a
client instance at runtime through the Section 3.5 or MAY be obtained
in another fashion, such as a static registration process at the AS.
"client": "client-541-ab"
When the AS receives a request with an instance identifier, the AS
MUST ensure that the key used to sign the request (Section 7.3) is
associated with the instance identifier.
If the AS does not recognize the instance identifier, the request
MUST be rejected with an error.
If the client instance is identified in this manner, the registered
key for the client instance MAY be a symmetric key known to the AS.
The client instance MUST NOT send a symmetric key by value in the
request, as doing so would expose the key directly instead of proving
possession of it.
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2.3.2. Providing Displayable Client Instance Information
If the client instance has additional information to display to the
RO during any interactions at the AS, it MAY send that information in
the "display" field. This field is a JSON object that declares
information to present to the RO during any interactive sequences.
name (string) Display name of the client software
uri (string) User-facing web page of the client software
logo_uri (string) Display image to represent the client software
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
}
[[ See issue #48 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/48) ]]
Additional display fields are defined by a registry TBD (Section 11).
The AS SHOULD use these values during interaction with the RO. The
values are for informational purposes only and MUST NOT be taken as
authentic proof of the client instance's identity or source. The AS
MAY restrict display values to specific client instances, as
identified by their keys in Section 2.3.
2.3.3. Authenticating the Client Instance
If the presented key is known to the AS and is associated with a
single instance of the client software, the process of presenting a
key and proving possession of that key is sufficient to authenticate
the client instance to the AS. The AS MAY associate policies with
the client instance identified by this key, such as limiting which
resources can be requested and which interaction methods can be used.
For example, only specific client instances with certain known keys
might be trusted with access tokens without the AS interacting
directly with the RO as in Appendix D.3.
The presentation of a key allows the AS to strongly associate
multiple successive requests from the same client instance with each
other. This is true when the AS knows the key ahead of time and can
use the key to authenticate the client instance, but also if the key
is ephemeral and created just for this series of requests. As such
the AS MAY allow for client instances to make requests with unknown
keys. This pattern allows for ephemeral client instances, such as
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single-page applications, and client software with many individual
long-lived instances, such as mobile applications, to generate key
pairs per instance and use the keys within the protocol without
having to go through a separate registration step. The AS MAY limit
which capabilities are made available to client instances with
unknown keys. For example, the AS could have a policy saying that
only previously-registered client instances can request particular
resources, or that all client instances with unknown keys have to be
interactively approved by an RO.
2.4. Identifying the User
If the client instance knows the identity of the end-user through one
or more identifiers or assertions, the client instance MAY send that
information to the AS in the "user" field. The client instance MAY
pass this information by value or by reference.
sub_ids (array of objects) An array of subject identifiers for the
end-user, as defined by [I-D.ietf-secevent-subject-identifiers].
assertions (object) An object containing assertions as values keyed
on the assertion type defined by a registry TBD (Section 11).
Possible keys include "id_token" for an [OIDC] ID Token and
"saml2" for a SAML 2 assertion. Additional assertion values are
defined by a registry TBD (Section 11). [[ See issue #41
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/41) ]]
"user": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ],
"assertions": {
"id_token": "eyj..."
}
}
Subject identifiers are hints to the AS in determining the RO and
MUST NOT be taken as declarative statements that a particular RO is
present at the client instance and acting as the end-user.
Assertions SHOULD be validated by the AS. [[ See issue #49
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/49) ]]
If the identified end-user does not match the RO present at the AS
during an interaction step, the AS SHOULD reject the request with an
error.
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[[ See issue #50 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/50) ]]
If the AS trusts the client instance to present verifiable
assertions, the AS MAY decide, based on its policy, to skip
interaction with the RO, even if the client instance provides one or
more interaction modes in its request.
2.4.1. Identifying the User by Reference
The AS can identify the current end-user to the client instance with
a reference which can be used by the client instance to refer to the
end-user across multiple requests. If the client instance has a
reference for the end-user at this AS, the client instance MAY pass
that reference as a string. The format of this string is opaque to
the client instance.
"user": "XUT2MFM1XBIKJKSDU8QM"
One means of dynamically obtaining such a user reference is from the
AS returning an "opaque" subject identifier as described in
Section 3.4. Other means of configuring a client instance with a
user identifier are out of scope of this specification.
User reference identifiers are not intended to be human-readable user
identifiers or structured assertions. For the client instance to
send either of these, use the full user request object (Section 2.4)
instead.
If the AS does not recognize the user reference, it MUST return an
error.
2.5. Interacting with the User
Often, the AS will require interaction with the RO (Section 4) in
order to approve a requested delegation to the client instance for
both access to resources and direct subject information. Many times
the end-user using the client instance is the same person as the RO,
and the client instance can directly drive interaction with the end
user by facilitating the process through means such as redirection to
a URL or launching an application. Other times, the client instance
can provide information to start the RO's interaction on a secondary
device, or the client instance will wait for the RO to approve the
request asynchronously. The client instance could also be signaled
that interaction has concluded through a callback mechanism.
The client instance declares the parameters for interaction methods
that it can support using the "interact" field.
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The "interact" field is a JSON object with three keys whose values
declare how the client can initiate and complete the request, as well
as provide hints to the AS about user preferences such as locale. A
client instance MUST NOT declare an interaction mode it does not
support. The client instance MAY send multiple modes in the same
request. There is no preference order specified in this request. An
AS MAY respond to any, all, or none of the presented interaction
modes (Section 3.3) in a request, depending on its capabilities and
what is allowed to fulfill the request.
start (list of strings/objects) Indicates how the client instance
can start an interaction.
finish (object) Indicates how the client instance can receive an
indication that interaction has finished at the AS.
hints (object) Provides additional information to inform the
interaction process at the AS.
The "interact" field MUST contain the "start" key, and MAY contain
the "finish" and "hints" keys. The value of each key is an array
which contains strings or JSON objects as defined below.
In this non-normative example, the client instance is indicating that
it can redirect (Section 2.5.1.1) the end-user to an arbitrary URL
and can receive a redirect (Section 2.5.2.1) through a browser
request.
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
In this non-normative example, the client instance is indicating that
it can display a user code (Section 2.5.1.3) and direct the end-user
to an arbitrary URL (Section 2.5.1.1) on a secondary device, but it
cannot accept a redirect or push callback.
"interact": {
"start": ["redirect", "user_code"]
}
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If the client instance does not provide a suitable interaction
mechanism, the AS cannot contact the RO asynchronously, and the AS
determines that interaction is required, then the AS SHOULD return an
error since the client instance will be unable to complete the
request without authorization.
The AS SHOULD apply suitable timeouts to any interaction mechanisms
provided, including user codes and redirection URLs. The client
instance SHOULD apply suitable timeouts to any callback URLs.
2.5.1. Start Mode Definitions
This specification defines the following interaction start modes as
an array of string values under the "start" key:
"redirect" Indicates that the client instance can direct the end-
user to an arbitrary URL for interaction. Section 2.5.1.1
"app" Indicates that the client instance can launch an application
on the end-user's device for interaction. Section 2.5.1.2
"user_code" Indicates that the client instance can communicate a
human-readable short code to the end-user for use with a stable
URL. Section 2.5.1.3
2.5.1.1. Redirect to an Arbitrary URL
If the client instance is capable of directing the end-user to a URL
defined by the AS at runtime, the client instance indicates this by
sending the "redirect" field with the boolean value "true". The
means by which the client instance will activate this URL is out of
scope of this specification, but common methods include an HTTP
redirect, launching a browser on the end-user's device, providing a
scannable image encoding, and printing out a URL to an interactive
console. While this URL is generally hosted at the AS, the client
instance can make no assumptions about its contents, composition, or
relationship to the AS grant URL.
"interact": {
"start": ["redirect"]
}
If this interaction mode is supported for this client instance and
request, the AS returns a redirect interaction response
Section 3.3.1. The client instance manages this interaction method
as described in Section 4.1.1.
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2.5.1.2. Open an Application-specific URL
If the client instance can open a URL associated with an application
on the end-user's device, the client instance indicates this by
sending the "app" field with boolean value "true". The means by
which the client instance determines the application to open with
this URL are out of scope of this specification.
"interact": {
"start": ["app"]
}
If this interaction mode is supported for this client instance and
request, the AS returns an app interaction response with an app URL
payload Section 3.3.2. The client instance manages this interaction
method as described in Section 4.1.3.
[[ See issue #54 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/54) ]]
2.5.1.3. Display a Short User Code
If the client instance is capable of displaying or otherwise
communicating a short, human-entered code to the RO, the client
instance indicates this by sending the "user_code" field with the
boolean value "true". This code is to be entered at a static URL
that does not change at runtime. While this URL is generally hosted
at the AS, the client instance can make no assumptions about its
contents, composition, or relationship to the AS grant URL.
"interact": {
"start": ["user_code"]
}
If this interaction mode is supported for this client instance and
request, the AS returns a user code and interaction URL as specified
in Section 3.3.3. The client instances manages this interaction
method as described in Section 4.1.2
2.5.2. Finish Interaction Modes
If the client instance is capable of receiving a message from the AS
indicating that the RO has completed their interaction, the client
instance indicates this by sending the following members of an object
under the "finish" key.
method (string) REQUIRED. The callback method that the AS will use
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to contact the client instance. This specification defines the
following interaction completion methods, with other values
defined by a registry TBD (Section 11):
"redirect" Indicates that the client instance can receive a
redirect from the end-user's device after interaction with the
RO has concluded. Section 2.5.2.1
"push" Indicates that the client instance can receive an HTTP
POST request from the AS after interaction with the RO has
concluded. Section 2.5.2.2
uri (string) REQUIRED. Indicates the URI that the AS will either
send the RO to after interaction or send an HTTP POST request.
This URI MAY be unique per request and MUST be hosted by or
accessible by the client instance. This URI MUST NOT contain any
fragment component. This URI MUST be protected by HTTPS, be
hosted on a server local to the RO's browser ("localhost"), or use
an application-specific URI scheme. If the client instance needs
any state information to tie to the front channel interaction
response, it MUST use a unique callback URI to link to that
ongoing state. The allowable URIs and URI patterns MAY be
restricted by the AS based on the client instance's presented key
information. The callback URI SHOULD be presented to the RO
during the interaction phase before redirect.
nonce (string) REQUIRED. Unique value to be used in the calculation
of the "hash" query parameter sent to the callback URL, must be
sufficiently random to be unguessable by an attacker. MUST be
generated by the client instance as a unique value for this
request.
hash_method (string) OPTIONAL. The hash calculation mechanism to be
used for the callback hash in Section 4.2.3. Can be one of "sha3"
or "sha2". If absent, the default value is "sha3". [[ See issue
#56 (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/56)
]]
If this interaction mode is supported for this client instance and
request, the AS returns a nonce for use in validating the callback
response (Section 3.3.4). Requests to the callback URI MUST be
processed as described in Section 4.2, and the AS MUST require
presentation of an interaction callback reference as described in
Section 5.1.
[[ See issue #58 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/58) ]]
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[[ See issue #59 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/59) ]]
2.5.2.1. Receive an HTTP Callback Through the Browser
A finish "method" value of "redirect" indicates that the client
instance will expect a request from the RO's browser using the HTTP
method GET as described in Section 4.2.1.
"interact": {
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
Requests to the callback URI MUST be processed by the client instance
as described in Section 4.2.1.
Since the incoming request to the callback URL is from the RO's
browser, this method is usually used when the RO and end-user are the
same entity. As such, the client instance MUST ensure the end-user
is present on the request to prevent substitution attacks.
2.5.2.2. Receive an HTTP Direct Callback
A finish "method" value of "push" indicates that the client instance
will expect a request from the AS directly using the HTTP method POST
as described in Section 4.2.2.
"interact": {
"finish": {
"method": "push",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
Requests to the callback URI MUST be processed by the client instance
as described in Section 4.2.2.
Since the incoming request to the callback URL is from the AS and not
from the RO's browser, the client instance MUST NOT require the end-
user to be present on the incoming HTTP request.
[[ See issue #60 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/60) ]]
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2.5.3. Hints
The "hints" key is an object describing one or more suggestions from
the client instance that the AS can use to help drive user
interaction.
This specification defines the following properties under the "hints"
key:
ui_locales (array of strings) Indicates the end-user's preferred
locales that the AS can use during interaction, particularly
before the RO has authenticated. Section 2.5.3.1
The following sections detail requests for interaction modes.
Additional interaction modes are defined in a registry TBD
(Section 11).
2.5.3.1. Indicate Desired Interaction Locales
If the client instance knows the end-user's locale and language
preferences, the client instance can send this information to the AS
using the "ui_locales" field with an array of locale strings as
defined by [RFC5646].
"interact": {
"hints": {
"ui_locales": ["en-US", "fr-CA"]
}
}
If possible, the AS SHOULD use one of the locales in the array, with
preference to the first item in the array supported by the AS. If
none of the given locales are supported, the AS MAY use a default
locale.
2.5.4. Extending Interaction Modes
Additional interaction start modes, finish modes, and hints are
defined in a registry TBD (Section 11).
2.6. Extending The Grant Request
The request object MAY be extended by registering new items in a
registry TBD (Section 11). Extensions SHOULD be orthogonal to other
parameters. Extensions MUST document any aspects where the extension
item affects or influences the values or behavior of other request
and response objects.
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3. Grant Response
In response to a client instance's request, the AS responds with a
JSON object as the HTTP entity body. Each possible field is detailed
in the sections below
continue (object) Indicates that the client instance can continue
the request by making one or more continuation requests.
Section 3.1
access_token (object / array of objects) A single access token or
set of access tokens that the client instance can use to call the
RS on behalf of the RO. Section 3.2.1
interact (object) Indicates that interaction through some set of
defined mechanisms needs to take place. Section 3.3
subject (object) Claims about the RO as known and declared by the
AS, as described in Section 3.4.
instance_id (string) An identifier this client instance can use to
identify itself when making future requests. Section 3.5
error (object) An error code indicating that something has gone
wrong. Section 3.6
In this example, the AS is returning an interaction URL
(Section 3.3.1), a callback nonce (Section 3.3.4), and a continuation
response (Section 3.1).
NOTE: '\' line wrapping per RFC 8792
{
"interact": {
"redirect": "https://server.example.com/interact/4CF492ML\
VMSW9MKMXKHQ",
"finish": "MBDOFXG4Y5CVJCX821LH"
},
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU",
},
"uri": "https://server.example.com/tx"
}
}
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In this example, the AS is returning a bearer access token
(Section 3.2.1) with a management URL and a subject identifier
(Section 3.4) in the form of an opaque identifier.
NOTE: '\' line wrapping per RFC 8792
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"flags": ["bearer"],
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
},
"subject": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ]
}
}
In this example, the AS is returning set of subject identifiers
(Section 3.4), simultaneously as an opaque identifier, an email
address, and a decentralized identifier (DID).
{
"subject": {
"sub_ids": [ {
"subject_type": "opaque",
"id": "J2G8G8O4AZ"
}, {
"format": "email",
"email": "user@example.com"
}, {
"format": "did",
"url": "did:example:123456"
} ]
}
}
3.1. Request Continuation
If the AS determines that the request can be continued with
additional requests, it responds with the "continue" field. This
field contains a JSON object with the following properties.
uri (string) REQUIRED. The URI at which the client instance can
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make continuation requests. This URI MAY vary per request, or MAY
be stable at the AS if the AS includes an access token. The
client instance MUST use this value exactly as given when making a
continuation request (Section 5).
wait (integer) RECOMMENDED. The amount of time in integer seconds
the client instance SHOULD wait after receiving this continuation
handle and calling the URI.
access_token (object) REQUIRED. A unique access token for
continuing the request, in the format specified in Section 3.2.1.
This access token MUST be bound to the client instance's key used
in the request and MUST NOT be a "bearer" token. As a
consequence, the "flags" array of this access token MUST NOT
contain the string "bearer" and the "key" field MUST be omitted.
This access token MUST NOT be usable at resources outside of the
AS. The client instance MUST present the access token in all
requests to the continuation URI as described in Section 7.2. [[
See issue #66 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/66) ]]
{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 60
}
}
The client instance can use the values of this field to continue the
request as described in Section 5. Note that the client instance
MUST sign all continuation requests with its key as described in
Section 7.3 and MUST present the access token in its continuation
request.
This field SHOULD be returned when interaction is expected, to allow
the client instance to follow up after interaction has been
concluded.
3.2. Access Tokens
If the AS has successfully granted one or more access tokens to the
client instance, the AS responds with the "access_token" field. This
field contains either a single access token as described in
Section 3.2.1 or an array of access tokens as described in
Section 3.2.2.
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The client instance uses any access tokens in this response to call
the RS as described in Section 7.2.
3.2.1. Single Access Token
If the client instance has requested a single access token and the AS
has granted that access token, the AS responds with the
"access_token" field. The value of this field is an object with the
following properties.
value (string) REQUIRED. The value of the access token as a string.
The value is opaque to the client instance. The value SHOULD be
limited to ASCII characters to facilitate transmission over HTTP
headers within other protocols without requiring additional
encoding.
label (string) REQUIRED for multiple access tokens, OPTIONAL for
single access token. The value of the "label" the client instance
provided in the associated token request (Section 2.1), if
present. If the token has been split by the AS, the value of the
"label" field is chosen by the AS and the "split" field is
included and set to "true".
manage (string) OPTIONAL. The management URI for this access token.
If provided, the client instance MAY manage its access token as
described in Section 6. This management URI is a function of the
AS and is separate from the RS the client instance is requesting
access to. This URI MUST NOT include the access token value and
SHOULD be different for each access token issued in a request.
access (array of objects/strings) RECOMMENDED. A description of the
rights associated with this access token, as defined in Section 8.
If included, this MUST reflect the rights associated with the
issued access token. These rights MAY vary from what was
requested by the client instance.
expires_in (integer) OPTIONAL. The number of seconds in which the
access will expire. The client instance MUST NOT use the access
token past this time. An RS MUST NOT accept an access token past
this time. Note that the access token MAY be revoked by the AS or
RS at any point prior to its expiration.
key (object / string) OPTIONAL. The key that the token is bound to,
if different from the client instance's presented key. The key
MUST be an object or string in a format described in Section 7.1.
The client instance MUST be able to dereference or process the key
information in order to be able to sign the request.
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flags (array of strings) OPTIONAL. A set of flags that represent
attributes or behaviors of the access token issued by the AS.
The values of the "flags" field defined by this specification are as
follows:
"bearer" This flag indicates whether the token is bound to the
client instance's key. If the "bearer" flag is present, the
access token is a bearer token, and the "key" field in this
response MUST be omitted. If the "bearer" flag is omitted and the
"key" field in this response is omitted, the token is bound the
key used by the client instance (Section 2.3) in its request for
access. If the "bearer" flag is omitted, and the "key" field is
present, the token is bound to the key and proofing mechanism
indicated in the "key" field.
"durable" OPTIONAL. Flag indicating a hint of AS behavior on token
rotation. If this flag is present, then the client instance can
expect a previously-issued access token to continue to work after
it has been rotated (Section 6.1) or the underlying grant request
has been modified (Section 5.3), resulting in the issuance of new
access tokens. If this flag is omitted, the client instance can
anticipate a given access token will stop working after token
rotation or grant request modification. Note that a token flagged
as "durable" can still expire or be revoked through any normal
means.
"split" OPTIONAL. Flag indicating that this token was generated by
issuing multiple access tokens in response to one of the client
instance's token request (Section 2.1) objects. This behavior
MUST NOT be used unless the client instance has specifically
requested it by use of the "split" flag.
Flag values MUST NOT be included more than once.
Additional flags can be defined by extensions using a registry TBD
(Section 11).
The following non-normative example shows a single access token bound
to the client instance's key used in the initial request, with a
management URL, and that has access to three described resources (one
using an object and two described by reference strings).
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NOTE: '\' line wrapping per RFC 8792
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read", "dolphin-metadata"
]
}
The following non-normative example shows a single bearer access
token with access to two described resources.
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"flags": ["bearer"],
"access": [
"finance", "medical"
]
}
If the client instance requested a single access token
(Section 2.1.1), the AS MUST NOT respond with the multiple access
token structure unless the client instance sends the "split" flag as
described in Section 2.1.1.
If the AS has split the access token response, the response MUST
include the "split" flag.
[[ See issue #69 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/69) ]]
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3.2.2. Multiple Access Tokens
If the client instance has requested multiple access tokens and the
AS has granted at least one of them, the AS responds with the
"access_token" field. The value of this field is a JSON array, the
members of which are distinct access tokens as described in
Section 3.2.1. Each object MUST have a unique "label" field,
corresponding to the token labels chosen by the client instance in
the multiple access token request (Section 2.1.2).
In this non-normative example, two tokens are issued under the names
"token1" and "token2", and only the first token has a management URL
associated with it.
NOTE: '\' line wrapping per RFC 8792
"access_token": [
{
"label": "token1",
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [ "finance" ]
},
{
"label": "token2",
"value": "UFGLO2FDAFG7VGZZPJ3IZEMN21EVU71FHCARP4J1",
"access": [ "medical" ]
}
}
Each access token corresponds to one of the objects in the
"access_token" array of the client instance's request
(Section 2.1.2).
The multiple access token response MUST be used when multiple access
tokens are requested, even if only one access token is issued as a
result of the request. The AS MAY refuse to issue one or more of the
requested access tokens, for any reason. In such cases the refused
token is omitted from the response and all of the other issued access
tokens are included in the response the requested names appropriate
names.
If the client instance requested multiple access tokens
(Section 2.1.2), the AS MUST NOT respond with a single access token
structure, even if only a single access token is granted. In such
cases, the AS responds with a multiple access token structure
containing one access token.
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If the AS has split the access token response, the response MUST
include the "split" flag in the "flags" array.
"access_token": [
{
"label": "split-1",
"value": "8N6BW7OZB8CDFONP219-OS9M2PMHKUR64TBRP1LT0",
"flags": ["split"],
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [ "fruits" ]
},
{
"label": "split-2",
"value": "FG7VGZZPJ3IZEMN21EVU71FHCAR-UFGLO2FDAP4J1",
"flags": ["split"],
"access": [ "vegetables" ]
}
}
Each access token MAY be bound to different keys with different
proofing mechanisms.
If token management (Section 6) is allowed, each access token SHOULD
have different "manage" URIs.
[[ See issue #70 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/70) ]]
3.3. Interaction Modes
If the client instance has indicated a capability to interact with
the RO in its request (Section 2.5), and the AS has determined that
interaction is both supported and necessary, the AS responds to the
client instance with any of the following values in the "interact"
field of the response. There is no preference order for interaction
modes in the response, and it is up to the client instance to
determine which ones to use. All supported interaction methods are
included in the same "interact" object.
redirect (string) Redirect to an arbitrary URL. Section 3.3.1
app (string) Launch of an application URL. Section 3.3.2
finish (string) A nonce used by the client instance to verify the
callback after interaction is completed. Section 3.3.4
user_code (object) Display a short user code. Section 3.3.3
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Additional interaction mode responses can be defined in a registry
TBD (Section 11).
The AS MUST NOT respond with any interaction mode that the client
instance did not indicate in its request. The AS MUST NOT respond
with any interaction mode that the AS does not support. Since
interaction responses include secret or unique information, the AS
SHOULD respond to each interaction mode only once in an ongoing
request, particularly if the client instance modifies its request
(Section 5.3).
3.3.1. Redirection to an arbitrary URL
If the client instance indicates that it can redirect to an arbitrary
URL (Section 2.5.1.1) and the AS supports this mode for the client
instance's request, the AS responds with the "redirect" field, which
is a string containing the URL to direct the end-user to. This URL
MUST be unique for the request and MUST NOT contain any security-
sensitive information such as user identifiers or access tokens.
"interact": {
"redirect": "https://interact.example.com/4CF492MLVMSW9MKMXKHQ"
}
The URL returned is a function of the AS, but the URL itself MAY be
completely distinct from the URL the client instance uses to request
access (Section 2), allowing an AS to separate its user-interactive
functionality from its back-end security functionality. If the AS
does not directly host the functionality accessed through the given
URL, then the means for the interaction functionality to communicate
with the rest of the AS are out of scope for this specification.
[[ See issue #72 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/72) ]]
The client instance sends the end-user to the URL to interact with
the AS. The client instance MUST NOT alter the URL in any way. The
means for the client instance to send the end-user to this URL is out
of scope of this specification, but common methods include an HTTP
redirect, launching the system browser, displaying a scannable code,
or printing out the URL in an interactive console. See details of
the interaction in Section 4.1.1.
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3.3.2. Launch of an application URL
If the client instance indicates that it can launch an application
URL (Section 2.5.1.2) and the AS supports this mode for the client
instance's request, the AS responds with the "app" field, which is a
string containing the URL for the client instance to launch. This
URL MUST be unique for the request and MUST NOT contain any security-
sensitive information such as user identifiers or access tokens.
"interact": {
"app": "https://app.example.com/launch?tx=4CF492MLV"
}
The means for the launched application to communicate with the AS are
out of scope for this specification.
The client instance launches the URL as appropriate on its platform,
and the means for the client instance to launch this URL is out of
scope of this specification. The client instance MUST NOT alter the
URL in any way. The client instance MAY attempt to detect if an
installed application will service the URL being sent before
attempting to launch the application URL. See details of the
interaction in Section 4.1.3.
[[ See issue #71 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/71) ]]
3.3.3. Display of a Short User Code
If the client instance indicates that it can display a short
user-typeable code (Section 2.5.1.3) and the AS supports this mode
for the client instance's request, the AS responds with a "user_code"
field. This field is an object that contains the following members.
code (string) REQUIRED. A unique short code that the user can type
into an authorization server. This string MUST be case-
insensitive, MUST consist of only easily typeable characters (such
as letters or numbers). The time in which this code will be
accepted SHOULD be short lived, such as several minutes. It is
RECOMMENDED that this code be no more than eight characters in
length.
url (string) RECOMMENDED. The interaction URL that the client
instance will direct the RO to. This URL MUST be stable such that
client instances can be statically configured with it.
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"interact": {
"user_code": {
"code": "A1BC-3DFF",
"url": "https://srv.ex/device"
}
}
The client instance MUST communicate the "code" to the end-user in
some fashion, such as displaying it on a screen or reading it out
audibly.
The client instance SHOULD also communicate the URL if possible to
facilitate user interaction, but since the URL should be stable, the
client instance should be able to safely decide to not display this
value. As this interaction mode is designed to facilitate
interaction via a secondary device, it is not expected that the
client instance redirect the end-user to the URL given here at
runtime. Consequently, the URL needs to be stable enough that a
client instance could be statically configured with it, perhaps
referring the end-user to the URL via documentation instead of
through an interactive means. If the client instance is capable of
communicating an arbitrary URL to the end-user, such as through a
scannable code, the client instance can use the "redirect"
(Section 2.5.1.1) mode for this purpose instead of or in addition to
the user code mode.
The URL returned is a function of the AS, but the URL itself MAY be
completely distinct from the URL the client instance uses to request
access (Section 2), allowing an AS to separate its user-interactive
functionality from its back-end security functionality. If the AS
does not directly host the functionality accessed through the given
URL, then the means for the interaction functionality to communicate
with the rest of the AS are out of scope for this specification.
See details of the interaction in Section 4.1.2.
[[ See issue #72 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/72) ]]
3.3.4. Interaction Finish
If the client instance indicates that it can receive a
post-interaction redirect or push at a URL (Section 2.5.2) and the AS
supports this mode for the client instance's request, the AS responds
with a "finish" field containing a nonce that the client instance
will use in validating the callback as defined in Section 4.2.
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"interact": {
"finish": "MBDOFXG4Y5CVJCX821LH"
}
When the interaction is completed, the interaction component MUST
contact the client instance using either a redirect or launch of the
RO's browser or through an HTTP POST to the client instance's
callback URL using the method indicated in the interaction request
(Section 2.5.2) as described in Section 4.2.
If the AS returns a nonce, the client instance MUST NOT continue a
grant request before it receives the associated interaction reference
on the callback URI. See details in Section 4.2.
3.3.5. Extending Interaction Mode Responses
Extensions to this specification can define new interaction mode
responses in a registry TBD (Section 11). Extensions MUST document
the corresponding interaction request.
3.4. Returning Subject Information
If information about the RO is requested and the AS grants the client
instance access to that data, the AS returns the approved information
in the "subject" response field. The AS MUST return the "subject"
field only in cases where the AS is sure that the RO and the end-user
are the same party. This can be accomplished through some forms of
interaction with the RO (Section 4).
This field is an object with the following OPTIONAL properties.
sub_ids (array of objects) An array of subject identifiers for the
RO, as defined by [I-D.ietf-secevent-subject-identifiers].
assertions (object) An object containing assertions as values keyed
on the assertion type defined by a registry TBD (Section 11). [[
See issue #41 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/41) ]]
updated_at (string) Timestamp as an ISO8610 date string, indicating
when the identified account was last updated. The client instance
MAY use this value to determine if it needs to request updated
profile information through an identity API. The definition of
such an identity API is out of scope for this specification.
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"subject": {
"sub_ids": [ {
"format": "opaque",
"id": "XUT2MFM1XBIKJKSDU8QM"
} ],
"assertions": {
"id_token": "eyj..."
}
}
Subject identifiers returned by the AS SHOULD uniquely identify the
RO at the AS. Some forms of subject identifier are opaque to the
client instance (such as the subject of an issuer and subject pair),
while others forms (such as email address and phone number) are
intended to allow the client instance to correlate the identifier
with other account information at the client instance. The AS MUST
ensure that the returned subject identifiers only apply to the
authenticated end user. The client instance MUST NOT request or use
any returned subject identifiers for communication purposes (see
Section 2.2). That is, a subject identifier returned in the format
of an email address or a phone number only identifies the RO to the
AS and does not indicate that the AS has validated that the
represented email address or phone number in the identifier is
suitable for communication with the current user. To get such
information, the client instance MUST use an identity protocol to
request and receive additional identity claims. The details of an
identity protocol and associated schema are outside the scope of this
specification.
Extensions to this specification MAY define additional response
properties in a registry TBD (Section 11).
3.5. Returning Dynamically-bound Reference Handles
Many parts of the client instance's request can be passed as either a
value or a reference. The use of a reference in place of a value
allows for a client instance to optimize requests to the AS.
Some references, such as for the client instance's identity
(Section 2.3.1) or the requested resources (Section 8.1), can be
managed statically through an admin console or developer portal
provided by the AS or RS. The developer of the client software can
include these values in their code for a more efficient and compact
request.
If desired, the AS MAY also generate and return some of these
references dynamically to the client instance in its response to
facilitate multiple interactions with the same software. The client
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instance SHOULD use these references in future requests in lieu of
sending the associated data value. These handles are intended to be
used on future requests.
Dynamically generated handles are string values that MUST be
protected by the client instance as secrets. Handle values MUST be
unguessable and MUST NOT contain any sensitive information. Handle
values are opaque to the client instance.
All dynamically generated handles are returned as fields in the root
JSON object of the response. This specification defines the
following dynamic handle return, additional handles can be defined in
a registry TBD (Section 11).
instance_id (string) A string value used to represent the
information in the "client" object that the client instance can
use in a future request, as described in Section 2.3.1.
This non-normative example shows one handle along side an issued
access token.
{
"instance_id": "7C7C4AZ9KHRS6X63AJAO",
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0"
}
}
[[ See issue #77 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/77) ]]
[[ See issue #78 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/78) ]]
3.6. Error Response
If the AS determines that the request cannot be issued for any
reason, it responds to the client instance with an error message.
error (string) The error code.
{
"error": "user_denied"
}
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The error code is one of the following, with additional values
available in a registry TBD (Section 11):
user_denied The RO denied the request.
too_fast The client instance did not respect the timeout in the wait
response.
unknown_request The request referenced an unknown ongoing access
request.
[[ See issue #79 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/79) ]]
3.7. Extending the Response
Extensions to this specification MAY define additional fields for the
grant response in a registry TBD (Section 11).
4. Determining Authorization and Consent
When the client instance makes its Section 2 to the AS for delegated
access, it is capable of asking for several different kinds of
information in response:
* the access being requested in the "access_token" request parameter
* the subject information being requested in the "subject" request
parameter
* any additional requested information defined by extensions of this
protocol
The AS determines what authorizations and consents are required to
fulfill this requested delegation. The details of how the AS makes
this determination are out of scope for this document. However,
there are several common patterns defined and supported by GNAP for
fulfilling these requirements, including information sent by the
client instance, information gathered through the interaction
process, and information supplied by external parties. An individual
AS can define its own policies and processes for deciding when and
how to gather the necessary authorizations and consent.
The client instance can supply information directly to the AS in its
request. From this information, the AS can determine if the
requested delegation can be granted immediately. The client instance
can send several kinds of things, including:
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* the identity of the client instance, known from the presented keys
or associated identifiers
* the identity of the end user presented in the "user" request
parameter
* any additional information presented by the client instance in the
request, including any extensions
The AS will verify this presented information in the context of the
client instance's request and can only trust the information as much
as it trusts the presentation and context of the information. If the
AS determines that the information presented in the initial request
is sufficient for granting the requested access, the AS MAY return
the positive results immediately in its Section 3 with access tokens
and subject information.
If the AS determines that additional runtime authorization is
required, the AS can either deny the request outright or use a number
of means at its disposal to gather that authorization from the
appropriate ROs, including for example:
* starting interaction with the end user facilitated by the client
software, such as a redirection or user code
* challenging the client instance through a challenge-response
mechanism
* requesting that the client instance present specific additional
information, such as a user's credential or an assertion
* contacting a RO through an out-of-band mechanism, such as a push
notification
* contacting an auxiliary software process through an out-of-band
mechanism, such as querying a digital wallet
The authorization and consent gathering process in GNAP is left
deliberately flexible to allow for a wide variety of different
deployments, interactions, and methodologies. In this process, the
AS can gather consent from the RO as necessitated by the access that
has been requested. The AS can sometimes determine which RO needs to
consent based on what has been requested by the client instance, such
as a specific RS record, an identified user, or a request requiring
specific access such as approval by an administrator. If the AS has
a means of contacting the RO directly, it could do so without
involving the client instance in its consent gathering process. For
example, the AS could push a notification to a known RO and have the
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RO approve the pending request asynchronously. These interactions
can be through an interface of the AS itself (such as a hosted web
page), through another application (such as something installed on
the RO's device), through a messaging fabric, or any other means.
When interacting with an RO, the AS can do anything it needs to
determine the authorization of the requested grant, including:
* authenticate the RO, through a local account or some other means
such as federated login
* validate the RO through presentation of claims, attributes, or
other information
* prompt the RO for consent for the requested delegation
* describe to the RO what information is being released, to whom,
and for what purpose
* provide warnings to the RO about potential attacks or negative
effects of allowing the information
* allow the RO to modify the client instance's requested access,
including limiting or expanding that access
* provide the RO with artifacts such as receipts to facilitate an
audit trail of authorizations
* allow the RO to deny the requested delegation
The AS is also allowed to request authorization from more than one
RO, if the AS deems fit. For example, a medical record might need to
be released by both an attending nurse and a physician, or both
owners of a bank account need to sign off on a transfer request.
Alternatively, the AS could require N of M possible RO's to approve a
given request in order. The AS could also determine that the end
user is not the appropriate RO for a given request and reach out to
the appropriate RO asynchronously. The details of determining which
RO's are required for a given request are out of scope for this
specification.
The client instance can also indicate that it is capable of
facilitating interaction with the end user, another party, or another
piece of software through its interaction start (Section 2.5.1)
request. In many cases, the end user is delegating their own access
as RO to the client instance. Here, the AS needs to determine the
identity of the end user and will often need to interact directly
with the end user to determine their status as an RO and collect
their consent. If the AS has determined that authorization is
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required and the AS can support one or more of the requested
interaction start methods, the AS returns the associated interaction
start responses (Section 3.3). The client instance SHOULD initiate
one or more of these interaction methods (Section 4.1) in order to
facilitate the granting of the request. If more than one interaction
start method is available, the means by which the client chooses
which methods to follow is out of scope of this specification. The
client instance MUST use each interaction method once at most.
After starting interaction, the client instance can then make a
continuation request (Section 5) either in response to a signal
indicating the finish of the interaction (Section 4.2), through
polling, or through some other method defined by an extension of this
specification.
If the AS and client instance have not reached a state where the
delegation can be granted, the AS and client instance can repeat the
interaction process as long as the AS supplies the client instance
with continuation information (Section 3.1) to facilitate the ongoing
requests.
4.1. Interaction Start Methods
To initiate an interaction start method indicated by the interaction
start responses (Section 3.3) from the AS, the client instance
follows the steps defined by that interaction method. The actions of
the client instance required for the interaction start modes defined
in this specification are described in the following sections.
4.1.1. Interaction at a Redirected URI
When the end user is directed to an arbitrary URI through the
"redirect" (Section 3.3.1) mode, the client instance facilitates
opening the URI through the end user's web browser. The client
instance could launch the URI through the system browser, provide a
clickable link, redirect the user through HTTP response codes, or
display the URI in a form the end user can use to launch such as a
multidimensional barcode. With this method, it is common (though not
required) for the RO to be the same party as the end-user, since the
client instance has to communicate the redirection URI to the end-
user.
In many cases, the URI indicates a web page hosted at the AS,
allowing the AS to authenticate the end user as the RO and
interactively provide consent. If the URI is hosted by the AS, the
AS MUST determine the grant request being referenced from the URL
value itself. If the URL cannot be associated with a currently
active request, the AS MUST display an error to the RO and MUST NOT
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attempt to redirect the RO back to any client instance even if a
redirect finish method is supplied (Section 2.5.2.1). If the URI is
not hosted by the AS directly, the means of communication between the
AS and this URI are out of scope for this specification.
The client instance MUST NOT modify the URI when launching it, in
particular the client instance MUST NOT add any parameters to the
URI. The URI MUST be reachable from the end user's browser, though
the URI MAY be opened on a separate device from the client instance
itself. The URI MUST be accessible from an HTTP GET request and MUST
be protected by HTTPS or equivalent means.
4.1.2. Interaction at the User Code URI
When the end user is directed to enter a short code through the
"user_code" (Section 3.3.3) mode, the client instance communicates
the user code to the end-user and directs the end user to enter that
code at an associated URI. This mode is used when the client
instance is not able to facilitate launching an arbitrary URI. The
associated URI could be statically configured with the client
instance or communicated in the response from the AS, but the client
instance communicates that URL to the end user. As a consequence,
these URIs SHOULD be short.
In many cases, the URI indicates a web page hosted at the AS,
allowing the AS to authenticate the end user as the RO and
interactively provide consent. If the URI is hosted by the AS, the
AS MUST determine the grant request being referenced from the user
code. If the user code cannot be associated with a currently active
request, the AS MUST display an error to the RO and MUST NOT attempt
to redirect the RO back to any client instance even if a redirect
finish method is supplied (Section 2.5.2.1). If the interaction
component at the user code URI is not hosted by the AS directly, the
means of communication between the AS and this URI, including
communication of the user code itself, are out of scope for this
specification.
When the RO enters this code at the user code URI, the AS MUST
uniquely identify the pending request that the code was associated
with. If the AS does not recognize the entered code, the interaction
component MUST display an error to the user. If the AS detects too
many unrecognized code enter attempts, the interaction component
SHOULD display an error to the user and MAY take additional actions
such as slowing down the input interactions. The user should be
warned as such an error state is approached, if possible.
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The client instance MUST NOT modify the URI when launching it, in
particular the client instance MUST NOT add any parameters to the
URI. The user code URI MUST be reachable from the end user's
browser, though the URI is usually be opened on a separate device
from the client instance itself. The URI MUST be accessible from an
HTTP GET request and MUST be protected by HTTPS or equivalent means.
4.1.3. Interaction through an Application URI
When the client instance is directed to launch an application through
the "app" (Section 3.3.2) mode, the client launches the URL as
appropriate to the system, such as through a deep link or custom URI
scheme registered to a mobile application. The means by which the AS
and the launched application communicate with each other and perform
any of the required actions are out of scope for this specification.
4.2. Post-Interaction Completion
If an interaction "finish" (Section 3.3.4) method is associated with
the current request, the AS MUST follow the appropriate method at
upon completion of interaction in order to signal the client instance
to continue, except for some limited error cases discussed below. If
a finish method is not available, the AS SHOULD instruct the RO to
return to the client instance upon completion.
The AS MUST create an interaction reference and associate that
reference with the current interaction and the underlying pending
request. This interaction reference value MUST be sufficiently
random so as not to be guessable by an attacker. The interaction
reference MUST be one-time-use to prevent interception and replay
attacks.
The AS MUST calculate a hash value based on the client instance and
AS nonces and the interaction reference, as described in
Section 4.2.3. The client instance will use this value to validate
the "finish" call.
The AS MUST send the hash and interaction reference based on the
interaction finish mode as described in the following sections.
Note that the "finish" method still occurs in many error cases, such
as when the RO has denied access. This pattern allows the client
instance to potentially recover from the error state by modifying its
request or providing additional information directly to the AS in a
continuation request. The AS MUST NOT follow the "finish" method in
the following circumstances:
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* The AS has determined that any URIs involved with the finish
method are dangerous or blocked.
* The AS cannot determine which ongoing grant request is being
referenced.
* The ongoing grant request has been cancelled or otherwise blocked.
4.2.1. Completing Interaction with a Browser Redirect to the Callback
URI
When using the "redirect" interaction finish method (Section 3.3.4),
the AS signals to the client instance that interaction is complete
and the request can be continued by directing the RO (in their
browser) back to the client instance's redirect URL sent in the
callback request (Section 2.5.2.1).
The AS secures this redirect by adding the hash and interaction
reference as query parameters to the client instance's redirect URL.
hash REQUIRED. The interaction hash value as described in
Section 4.2.3.
interact_ref REQUIRED. The interaction reference generated for this
interaction.
The means of directing the RO to this URL are outside the scope of
this specification, but common options include redirecting the RO
from a web page and launching the system browser with the target URL.
NOTE: '\' line wrapping per RFC 8792
https://client.example.net/return/123455\
?hash=p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2\
HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A\
&interact_ref=4IFWWIKYBC2PQ6U56NL1
When receiving the request, the client instance MUST parse the query
parameters to calculate and validate the hash value as described in
Section 4.2.3. If the hash validates, the client instance sends a
continuation request to the AS as described in Section 5.1 using the
interaction reference value received here.
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4.2.2. Completing Interaction with a Direct HTTP Request Callback
When using the "callback" interaction mode (Section 3.3.4) with the
"push" method, the AS signals to the client instance that interaction
is complete and the request can be continued by sending an HTTP POST
request to the client instance's callback URL sent in the callback
request (Section 2.5.2.2).
The entity message body is a JSON object consisting of the following
two fields:
hash (string) REQUIRED. The interaction hash value as described in
Section 4.2.3.
interact_ref (string) REQUIRED. The interaction reference generated
for this interaction.
NOTE: '\' line wrapping per RFC 8792
POST /push/554321 HTTP/1.1
Host: client.example.net
Content-Type: application/json
{
"hash": "p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R\
2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A",
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
When receiving the request, the client instance MUST parse the JSON
object and validate the hash value as described in Section 4.2.3. If
the hash validates, the client instance sends a continuation request
to the AS as described in Section 5.1 using the interaction reference
value received here.
4.2.3. Calculating the interaction hash
The "hash" parameter in the request to the client instance's callback
URL ties the front channel response to an ongoing request by using
values known only to the parties involved. This security mechanism
allows the client instance to protect itself against several kinds of
session fixation and injection attacks. The AS MUST always provide
this hash, and the client instance MUST validate the hash when
received.
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To calculate the "hash" value, the party doing the calculation
creates a hash string by concatenating the following values in the
following order using a single newline ("\\n") character to separate
them:
* the "nonce" value sent by the client instance in the interaction
"finish" section of the initial request (Section 2.5.2)
* the AS's nonce value from the interaction finish response
(Section 3.3.4)
* the "interact_ref" returned from the AS as part of the interaction
finish method (Section 4.2)
* the grant endpoint URL the client instance used to make its
initial request (Section 2)
There is no padding or whitespace before or after any of the lines,
and no trailing newline character.
VJLO6A4CAYLBXHTR0KRO
MBDOFXG4Y5CVJCX821LH
4IFWWIKYBC2PQ6U56NL1
https://server.example.com/tx
The party then hashes this string with the appropriate algorithm
based on the "hash_method" parameter of the "callback". If the
"hash_method" value is not present in the client instance's request,
the algorithm defaults to "sha3".
[[ See issue #56 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/56) ]]
4.2.3.1. SHA3-512
The "sha3" hash method consists of hashing the input string with the
512-bit SHA3 algorithm. The byte array is then encoded using URL
Safe Base64 with no padding. The resulting string is the hash value.
NOTE: '\' line wrapping per RFC 8792
p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM\
7XHPAdJzTZMtKBsaraJ64A
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4.2.3.2. SHA2-512
The "sha2" hash method consists of hashing the input string with the
512-bit SHA2 algorithm. The byte array is then encoded using URL
Safe Base64 with no padding. The resulting string is the hash value.
NOTE: '\' line wrapping per RFC 8792
62SbcD3Xs7L40rjgALA-ymQujoh2LB2hPJyX9vlcr1H6ecChZ8BNKkG_HrOKP_Bp\
j84rh4mC9aE9x7HPBFcIHw
5. Continuing a Grant Request
While it is possible for the AS to return a Section 3 with all the
client instance's requested information (including access tokens
(Section 3.2) and direct user information (Section 3.4)), it's more
common that the AS and the client instance will need to communicate
several times over the lifetime of an access grant. This is often
part of facilitating interaction (Section 4), but it could also be
used to allow the AS and client instance to continue negotiating the
parameters of the original grant request (Section 2).
To enable this ongoing negotiation, the AS provides a continuation
API to the client software. The AS returns a "continue" field in the
response (Section 3.1) that contains information the client instance
needs to access this API, including a URI to access as well as an
access token to use during the continued requests.
The access token is initially bound to the same key and method the
client instance used to make the initial request. As a consequence,
when the client instance makes any calls to the continuation URL, the
client instance MUST present the access token as described in
Section 7.2 and present proof of the client instance's key (or its
most recent rotation) by signing the request as described in
Section 7.3. The AS MUST validate all keys presented by the client
instance or referenced in an ongoing request for each call within
that request.
[[ See issue #85 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/85) ]]
For example, here the client instance makes a POST request to a
unique URI and signs the request with HTTP Message Signatures:
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POST /continue/KSKUOMUKM HTTP/1.1
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Host: server.example.com
Signature-Input: sig1=...
Signature: sig1=...
The AS MUST be able to tell from the client instance's request which
specific ongoing request is being accessed, using a combination of
the continuation URL, the provided access token, and the client
instance identified by the key signature. If the AS cannot determine
a single active grant request to map the continuation request to, the
AS MUST return an error.
The ability to continue an already-started request allows the client
instance to perform several important functions, including presenting
additional information from interaction, modifying the initial
request, and getting the current state of the request.
All requests to the continuation API are protected by this bound
access token. For example, here the client instance makes a POST
request to a stable continuation endpoint URL with the interaction
reference (Section 5.1), includes the access token, and signs with
HTTP Message Signatures:
POST /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
If a "wait" parameter was included in the continuation response
(Section 3.1), the client instance MUST NOT call the continuation URI
prior to waiting the number of seconds indicated. If no "wait"
period is indicated, the client instance SHOULD wait at least 5
seconds. If the client instance does not respect the given wait
period, the AS MUST return an error. [[ See issue #86
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/86) ]]
The response from the AS is a JSON object and MAY contain any of the
fields described in Section 3, as described in more detail in the
sections below.
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If the AS determines that the client instance can make a further
continuation request, the AS MUST include a new "continue" response
(Section 3.1). The new "continue" response MUST include a bound
access token as well, and this token SHOULD be a new access token,
invalidating the previous access token. If the AS does not return a
new "continue" response, the client instance MUST NOT make an
additional continuation request. If a client instance does so, the
AS MUST return an error. [[ See issue #87 (https://github.com/ietf-
wg-gnap/gnap-core-protocol/issues/87) ]]
For continuation functions that require the client instance to send a
message body, the body MUST be a JSON object.
5.1. Continuing After a Completed Interaction
When the AS responds to the client instance's "finish" method as in
Section 4.2.1, this response includes an interaction reference. The
client instance MUST include that value as the field "interact_ref"
in a POST request to the continuation URI.
POST /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
Since the interaction reference is a one-time-use value as described
in Section 4.2.1, if the client instance needs to make additional
continuation calls after this request, the client instance MUST NOT
include the interaction reference. If the AS detects a client
instance submitting the same interaction reference multiple times,
the AS MUST return an error and SHOULD invalidate the ongoing
request.
The Section 3 MAY contain any newly-created access tokens
(Section 3.2) or newly-released subject claims (Section 3.4). The
response MAY contain a new "continue" response (Section 3.1) as
described above. The response SHOULD NOT contain any interaction
responses (Section 3.3). [[ See issue #89 (https://github.com/ietf-
wg-gnap/gnap-core-protocol/issues/89) ]]
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For example, if the request is successful in causing the AS to issue
access tokens and release opaque subject claims, the response could
look like this:
NOTE: '\' line wrapping per RFC 8792
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
},
"subject": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ]
}
}
With this example, the client instance can not make an additional
continuation request because a "continue" field is not included.
[[ See issue #88 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/88) ]]
5.2. Continuing During Pending Interaction
When the client instance does not include a "finish" parameter, the
client instance will often need to poll the AS until the RO has
authorized the request. To do so, the client instance makes a POST
request to the continuation URI as in Section 5.1, but does not
include a message body.
POST /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
The Section 3 MAY contain any newly-created access tokens
(Section 3.2) or newly-released subject claims (Section 3.4). The
response MAY contain a new "continue" response (Section 3.1) as
described above. If a "continue" field is included, it SHOULD
include a "wait" field to facilitate a reasonable polling rate by the
client instance. The response SHOULD NOT contain interaction
responses (Section 3.3).
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For example, if the request has not yet been authorized by the RO,
the AS could respond by telling the client instance to make another
continuation request in the future. In this example, a new, unique
access token has been issued for the call, which the client instance
will use in its next continuation request.
{
"continue": {
"access_token": {
"value": "33OMUKMKSKU80UPRY5NM"
},
"uri": "https://server.example.com/continue",
"wait": 30
}
}
[[ See issue #90 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/90) ]]
[[ See issue #91 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/91) ]]
If the request is successful in causing the AS to issue access tokens
and release subject claims, the response could look like this
example:
NOTE: '\' line wrapping per RFC 8792
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
},
"subject": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ]
}
}
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5.3. Modifying an Existing Request
The client instance might need to modify an ongoing request, whether
or not tokens have already been issued or claims have already been
released. In such cases, the client instance makes an HTTP PATCH
request to the continuation URI and includes any fields it needs to
modify. Fields that aren't included in the request are considered
unchanged from the original request.
The client instance MAY include the "access_token" and "subject"
fields as described in Section 2.1 and Section 2.2. Inclusion of
these fields override any values in the initial request, which MAY
trigger additional requirements and policies by the AS. For example,
if the client instance is asking for more access, the AS could
require additional interaction with the RO to gather additional
consent. If the client instance is asking for more limited access,
the AS could determine that sufficient authorization has been granted
to the client instance and return the more limited access rights
immediately. [[ See issue #92 (https://github.com/ietf-wg-gnap/gnap-
core-protocol/issues/92) ]]
The client instance MAY include the "interact" field as described in
Section 2.5. Inclusion of this field indicates that the client
instance is capable of driving interaction with the RO, and this
field replaces any values from a previous request. The AS MAY
respond to any of the interaction responses as described in
Section 3.3, just like it would to a new request.
The client instance MAY include the "user" field as described in
Section 2.4 to present new assertions or information about the end-
user. [[ See issue #93 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/93) ]]
The client instance MUST NOT include the "client" section of the
request. [[ See issue #94 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/94) ]]
The client instance MAY include post-interaction responses such as
described in Section 5.1. [[ See issue #95 (https://github.com/ietf-
wg-gnap/gnap-core-protocol/issues/95) ]]
Modification requests MUST NOT alter previously-issued access tokens.
Instead, any access tokens issued from a continuation are considered
new, separate access tokens. The AS MAY revoke existing access
tokens after a modification has occurred. [[ See issue #96
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/96) ]]
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If the modified request can be granted immediately by the AS, the
Section 3 MAY contain any newly-created access tokens (Section 3.2)
or newly-released subject claims (Section 3.4). The response MAY
contain a new "continue" response (Section 3.1) as described above.
If interaction can occur, the response SHOULD contain interaction
responses (Section 3.3) as well.
For example, a client instance initially requests a set of resources
using references:
POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": {
"access": [
"read", "write"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
},
"client": "987YHGRT56789IOLK"
}
Access is granted by the RO, and a token is issued by the AS. In its
final response, the AS includes a "continue" field, which includes a
separate access token for accessing the continuation API:
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{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 30
},
"access_token": {
"value": "RP1LT0-OS9M2P_R64TB",
"access": [
"read", "write"
]
}
}
This "continue" field allows the client instance to make an eventual
continuation call. In the future, the client instance realizes that
it no longer needs "write" access and therefore modifies its ongoing
request, here asking for just "read" access instead of both "read"
and "write" as before.
PATCH /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": {
"access": [
"read"
]
}
...
}
The AS replaces the previous "access" from the first request,
allowing the AS to determine if any previously-granted consent
already applies. In this case, the AS would likely determine that
reducing the breadth of the requested access means that new access
tokens can be issued to the client instance. The AS would likely
revoke previously-issued access tokens that had the greater access
rights associated with them, unless they had been issued with the
"durable" flag.
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{
"continue": {
"access_token": {
"value": "M33OMUK80UPRY5NMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 30
},
"access_token": {
"value": "0EVKC7-2ZKwZM_6N760",
"access": [
"read"
]
}
}
For another example, the client instance initially requests read-only
access but later needs to step up its access. The initial request
could look like this example.
POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": {
"access": [
"read"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
},
"client": "987YHGRT56789IOLK"
}
Access is granted by the RO, and a token is issued by the AS. In its
final response, the AS includes a "continue" field:
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{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 30
},
"access_token": {
"value": "RP1LT0-OS9M2P_R64TB",
"access": [
"read"
]
}
}
This allows the client instance to make an eventual continuation
call. The client instance later realizes that it now needs "write"
access in addition to the "read" access. Since this is an expansion
of what it asked for previously, the client instance also includes a
new interaction section in case the AS needs to interact with the RO
again to gather additional authorization. Note that the client
instance's nonce and callback are different from the initial request.
Since the original callback was already used in the initial exchange,
and the callback is intended for one-time-use, a new one needs to be
included in order to use the callback again.
[[ See issue #97 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
issues/97) ]]
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PATCH /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": {
"access": [
"read", "write"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/654321",
"nonce": "K82FX4T4LKLTI25DQFZC"
}
}
}
From here, the AS can determine that the client instance is asking
for more than it was previously granted, but since the client
instance has also provided a mechanism to interact with the RO, the
AS can use that to gather the additional consent. The protocol
continues as it would with a new request. Since the old access
tokens are good for a subset of the rights requested here, the AS
might decide to not revoke them. However, any access tokens granted
after this update process are new access tokens and do not modify the
rights of existing access tokens.
5.4. Canceling a Grant Request
If the client instance wishes to cancel an ongoing grant request, it
makes an HTTP DELETE request to the continuation URI.
DELETE /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
If the request is successfully cancelled, the AS responds with an
HTTP 202. The AS SHOULD revoke all associated access tokens.
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6. Token Management
If an access token response includes the "manage" parameter as
described in Section 3.2.1, the client instance MAY call this URL to
manage the access token with any of the actions defined in the
following sections. Other actions are undefined by this
specification.
The access token being managed acts as the access element for its own
management API. The client instance MUST present proof of an
appropriate key along with the access token.
If the token is sender-constrained (i.e., not a bearer token), it
MUST be sent with the appropriate binding for the access token
(Section 7.2).
If the token is a bearer token, the client instance MUST present
proof of the same key identified in the initial request (Section 2.3)
as described in Section 7.3.
The AS MUST validate the proof and assure that it is associated with
either the token itself or the client instance the token was issued
to, as appropriate for the token's presentation type.
6.1. Rotating the Access Token
The client instance makes an HTTP POST to the token management URI,
sending the access token in the appropriate header and signing the
request with the appropriate key.
POST /token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L HTTP/1.1
Host: server.example.com
Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
The AS validates that the token presented is associated with the
management URL, that the AS issued the token to the given client
instance, and that the presented key is appropriate to the token.
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If the access token has expired, the AS SHOULD honor the rotation
request to the token management URL since it is likely that the
client instance is attempting to refresh the expired token. To
support this, the AS MAY apply different lifetimes for the use of the
token in management vs. its use at an RS. An AS MUST NOT honor a
rotation request for an access token that has been revoked, either by
the AS or by the client instance through the token management URI
(Section 6.2).
If the token is validated and the key is appropriate for the request,
the AS MUST invalidate the current access token associated with this
URL, if possible, and return a new access token response as described
in Section 3.2.1, unless the "multi_token" flag is specified in the
request. The value of the access token MUST NOT be the same as the
current value of the access token used to access the management API.
The response MAY include an updated access token management URL as
well, and if so, the client instance MUST use this new URL to manage
the new access token. [[ See issue #101 (https://github.com/ietf-wg-
gnap/gnap-core-protocol/issues/101) ]]
[[ See issue #102 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/102) ]]
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{
"access_token": {
"value": "FP6A8H6HY37MH13CK76LBZ6Y1UADG6VEUPEER5H2",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read", "dolphin-metadata"
]
}
}
[[ See issue #103 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/103) ]]
6.2. Revoking the Access Token
If the client instance wishes to revoke the access token proactively,
such as when a user indicates to the client instance that they no
longer wish for it to have access or the client instance application
detects that it is being uninstalled, the client instance can use the
token management URI to indicate to the AS that the AS should
invalidate the access token for all purposes.
The client instance makes an HTTP DELETE request to the token
management URI, presenting the access token and signing the request
with the appropriate key.
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DELETE /token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L HTTP/1.1
Host: server.example.com
Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
Signature-Input: sig1=...
Signature: sig1=...
If the key presented is associated with the token (or the client
instance, in the case of a bearer token), the AS MUST invalidate the
access token, if possible, and return an HTTP 204 response code.
204 No Content
Though the AS MAY revoke an access token at any time for any reason,
the token management function is specifically for the client
instance's use. If the access token has already expired or has been
revoked through other means, the AS SHOULD honor the revocation
request to the token management URL as valid, since the end result is
still the token not being usable.
7. Securing Requests from the Client Instance
In GNAP, the client instance secures its requests to the AS and RS by
presenting an access token, presenting proof of a key that it
possesses, or both an access token and key proof together.
* When an access token is used with a key proof, this is a bound
token request. This type of request is used for calls to the RS
as well as the AS during negotiation.
* When a key proof is used with no access token, this is a non-
authorized signed request. This type of request is used for calls
to the AS to initiate a negotiation.
* When an access token is used with no key proof, this is a bearer
token request. This type of request is used only for calls to the
RS, and only with access tokens that are not bound to any key as
described in Section 3.2.1.
* When neither an access token nor key proof are used, this is an
unsecured request. This type of request is used optionally for
calls to the RS as part of an RS-first discovery process as
described in Section 9.1.
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7.1. Key Formats
Several different places in GNAP require the presentation of key
material by value. Proof of this key material MUST be bound to a
request, the nature of which varies with the location in the protocol
the key is used. For a key used as part of a client instance's
initial request in Section 2.3, the key value is the client
instance's public key, and proof of that key MUST be presented in
that request. For a key used as part of an access token response in
Section 3.2.1, the proof of that key MUST be used when presenting the
access token.
A key presented by value MUST be a public key in at least one
supported format. If a key is sent in multiple formats, all the key
format values MUST be equivalent. Note that while most formats
present the full value of the public key, some formats present a
value cryptographically derived from the public key.
proof (string) The form of proof that the client instance will use
when presenting the key. The valid values of this field and the
processing requirements for each are detailed in Section 7.3. The
"proof" field is REQUIRED.
jwk (object) The public key and its properties represented as a JSON
Web Key [RFC7517]. A JWK MUST contain the "alg" (Algorithm) and
"kid" (Key ID) parameters. The "alg" parameter MUST NOT be
"none". The "x5c" (X.509 Certificate Chain) parameter MAY be used
to provide the X.509 representation of the provided public key.
cert (string) PEM serialized value of the certificate used to sign
the request, with optional internal whitespace per [RFC7468]. The
PEM header and footer are optionally removed.
cert#S256 (string) The certificate thumbprint calculated as per
OAuth-MTLS [RFC8705] in base64 URL encoding. Note that this
format does not include the full public key.
Additional key formats are defined in a registry TBD (Section 11).
This non-normative example shows a single key presented in multiple
formats. This example key is intended to be used with the HTTP
Message Signatures ({{httpsig-binding}}) proofing mechanism, as
indicated by the "httpsig" value of the "proof" field.
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"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
},
"cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFA..."
}
7.1.1. Key References
Keys in GNAP can also be passed by reference such that the party
receiving the reference will be able to determine the appropriate
keying material for use in that part of the protocol.
"key": "S-P4XJQ_RYJCRTSU1.63N3E"
Keys referenced in this manner MAY be shared symmetric keys. The key
reference MUST NOT contain any unencrypted private or shared
symmetric key information.
Keys referenced in this manner MUST be bound to a single proofing
mechanism.
The means of dereferencing this value are out of scope for this
specification.
7.2. Presenting Access Tokens
The method the client instance uses to send an access token depends
on whether the token is bound to a key, and if so which proofing
method is associated with the key. This information is conveyed in
the "bound" and "key" parameters in the single (Section 3.2.1) and
multiple access tokens (Section 3.2.2) responses.
If the "flags" field does not contain the "bearer" flag and the "key"
is absent, the access token MUST be sent using the same key and
proofing mechanism that the client instance used in its initial
request (or its most recent rotation).
If the "flags" field does not contain the "bearer" flag and the "key"
value is an object as described in Section 7.1, the access token MUST
be sent using the key and proofing mechanism defined by the value of
the "proof" field within the key object.
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The access token MUST be sent using the HTTP "Authorization" request
header field and the "GNAP" authorization scheme along with a key
proof as described in Section 7.3 for the key bound to the access
token. For example, an "httpsig"-bound access token is sent as
follows:
Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
Signature-Input: sig1=(authorization);...
Signature: sig1=...
If the "flags" field contains the "bearer" flag, the access token is
a bearer token that MUST be sent using the "Authorization Request
Header Field" method defined in [RFC6750].
Authorization: Bearer OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
The "Form-Encoded Body Parameter" and "URI Query Parameter" methods
of [RFC6750] MUST NOT be used.
[[ See issue #104 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/104) ]]
The client software MUST reject as an error a situation where the
"flags" field contains the "bearer" flag and the "key" field is
present with any value.
7.3. Proving Possession of a Key with a Request
Any keys presented by the client instance to the AS or RS MUST be
validated as part of the request in which they are presented. The
type of binding used is indicated by the proof parameter of the key
object in Section 7.1. Values defined by this specification are as
follows:
httpsig HTTP Signing signature header
mtls Mutual TLS certificate verification
jwsd A detached JWS signature header
jws Attached JWS payload
Additional proofing methods are defined by a registry TBD
(Section 11).
All key binding methods used by this specification MUST cover all
relevant portions of the request, including anything that would
change the nature of the request, to allow for secure validation of
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the request. Relevant aspects include the URI being called, the HTTP
method being used, any relevant HTTP headers and values, and the HTTP
message body itself. The verifier of the signed message MUST
validate all components of the signed message to ensure that nothing
has been tampered with or substituted in a way that would change the
nature of the request. Key binding method definitions SHOULD
enumerate how these requirements are fulfilled.
When a key proofing mechanism is bound to an access token, the key
being presented MUST be the key associated with the access token and
the access token MUST be covered by the signature method of the
proofing mechanism.
The key binding methods in this section MAY be used by other
components making calls as part of GNAP, such as the extensions
allowing the RS to make calls to the AS defined in {{I-D.ietf-gnap-
resource-servers}}. To facilitate this extended use, the sections
below are defined in generic terms of the "sender" and "verifier" of
the HTTP message. In the core functions of GNAP, the "sender" is the
client instance and the "verifier" is the AS or RS, as appropriate.
When used for delegation in GNAP, these key binding mechanisms allow
the AS to ensure that the keys presented by the client instance in
the initial request are in control of the party calling any follow-up
or continuation requests. To facilitate this requirement, the
continuation response (Section 3.1) includes an access token bound to
the client instance's key (Section 2.3), and that key (or its most
recent rotation) MUST be proved in all continuation requests
Section 5. Token management requests Section 6 are similarly bound
to either the access token's own key or, in the case of bearer
tokens, the client instance's key.
[[ See issue #105 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/105) ]]
In the following sections, unless otherwise noted, the "RS256" JOSE
Signature Algorithm is applied using the following RSA key (presented
here in JWK format):
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NOTE: '\' line wrapping per RFC 8792
{
"kid": "gnap-rsa",
"p": "xS4-YbQ0SgrsmcA7xDzZKuVNxJe3pCYwdAe6efSy4hdDgF9-vhC5gjaRk\
i1wWuERSMW4Tv44l5HNrL-Bbj_nCJxr_HAOaesDiPn2PnywwEfg3Nv95Nn-\
eilhqXRaW-tJKEMjDHu_fmJBeemHNZI412gBnXdGzDVo22dvYoxd6GM",
"kty": "RSA",
"q": "rVdcT_uy-CD0GKVLGpEGRR7k4JO6Tktc8MEHkC6NIFXihk_6vAIOCzCD6\
LMovMinOYttpRndKoGTNdJfWlDFDScAs8C5n2y1STCQPRximBY-bw39-aZq\
JXMxOLyPjzuVgiTOCBIvLD6-8-mvFjXZk_eefD0at6mQ5qV3U1jZt88",
"d": "FHlhdTF0ozTliDxMBffT6aJVKZKmbbFJOVNten9c3lXKB3ux3NAb_D2dB\
7inp9EV23oWrDspFtvCvD9dZrXgRKMHofkEpo_SSvBZfgtH-OTkbY_TqtPF\
FLPKAw0JX5cFPnn4Q2xE4n-dQ7tpRCKl59vZLHBrHShr90zqzFp0AKXU5fj\
b1gC9LPwsFA2Fd7KXmI1drQQEVq9R-o18Pnn4BGQNQNjO_VkcJTiBmEIVT_\
KJRPdpVJAmbgnYWafL_hAfeb_dK8p85yurEVF8nCK5oO3EPrqB7IL4UqaEn\
5Sl3u0j8x5or-xrrAoNz-gdOv7ONfZY6NFoa-3f8q9wBAHUuQ",
"e": "AQAB",
"qi": "ogpNEkDKg22Rj9cDV_-PJBZaXMk66Fp557RT1tafIuqJRHEufSOYnsto\
bWPJ0gHxv1gVJw3gm-zYvV-wTMNgr2wVsBSezSJjPSjxWZtmT2z68W1DuvK\
kZy15vz7Jd85hmDlriGcXNCoFEUsGLWkpHH9RwPIzguUHWmTt8y0oXyI",
"dp": "dvCKGI2G7RLh3WyjoJ_Dr6hZ3LhXweB3YcY3qdD9BnxZ71mrLiMQg4c_\
EBnwqCETN_5sStn2cRc2JXnvLP3G8t7IFKHTT_i_TSTacJ7uT04MSa053Y3\
RfwbvLjRNPR0UKAE3ZxROUoIaVNuU_6-QMf8-2ilUv2GIOrCN87gP_Vk",
"alg": "RS256",
"dq": "iMZmELaKgT9_W_MRT-UfDWtTLeFjIGRW8aFeVmZk9R7Pnyt8rNzyN-IQ\
M40ql8u8J6vc2GmQGfokLlPQ6XLSCY68_xkTXrhoU1f-eDntkhP7L6XawSK\
Onv5F2H7wyBQ75HUmHTg8AK2B_vRlMyFKjXbVlzKf4kvqChSGEz4IjQ",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8BfYdHsFzAt\
YKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZGYX\
jHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZx\
e0jRETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0\
bunS0K3bA_3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kO\
zywzwPTuq-cVQDyEN7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
7.3.1. HTTP Message Signing
This method is indicated by "httpsig" in the "proof" field. The
sender creates an HTTP Message Signature as described in
[I-D.ietf-httpbis-message-signatures].
The covered content of the signature MUST include the following:
@request-target: the target of the HTTP request
digest: The Digest header as defined in [RFC3230]. When the request
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message has a body, the signer MUST calculate this header value
and the verifier MUST validate this header.
When the request is bound to an access token, the covered content
MUST also include:
authorization: The Authorization header used to present the access
token as discussed in Section 7.2.
Other covered content MAY also be included.
If the signer's key presented is a JWK, the "keyid" parameter of the
signature MUST be set to the "kid" value of the JWK, the signing
algorithm used MUST be the JWS algorithm denoted by the key's "alg"
field, and the explicit "alg" signature parameter MUST NOT be
included.
In this example, the message body is the following JSON object:
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{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"proof": "httpsig",
"key": {
"jwk": {
"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "RS256",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
}
}
This body is hashed for the Digest header using SHA-256 into the
following encoded value:
SHA-256=98QzyNVYpdgTrWBKpC4qFSCmmR+CrwwvUoiaDCSjKxw=
The HTTP message signature input string is calculated to be the
following:
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"@request-target": post /gnap
"host": server.example.com
"content-type": application/json
"digest": SHA-256=98QzyNVYpdgTrWBKpC4qFSCmmR+CrwwvUoiaDCSjKxw=
"content-length": 986
"@signature-params": ("@request-target" "host" "content-type" \
"digest" "content-length");created=1618884475;keyid="gnap-rsa"
This leads to the following full HTTP message request:
NOTE: '\' line wrapping per RFC 8792
POST /gnap HTTP/1.1
Host: server.example.com
Content-Type: application/json
Content-Length: 986
Digest: SHA-256=98QzyNVYpdgTrWBKpC4qFSCmmR+CrwwvUoiaDCSjKxw=
Signature-Input: sig1=("@request-target" "host" "content-type" \
"digest" "content-length");created=1618884475;keyid="gnap-rsa"
Signature: \
sig1=:axj8FLOvEWBcwh+Xk6VTTKXxqo4XNygleTDJ8h3ZJfi1sSmWrRtyo9RG/dc\
miZmdszRjWbg+/ixVZpA4BL3AOwEOxxtmHAXNB8uJ0I3tfbs6Suyk4sEo8zPr+MJq\
MjxdJEUgAQAy2AH+wg5a7CKq4IdLTulFK9njUIeG7MygHumeiumM3DbDQAHgF46dV\
q5UC6KJnqhGM1rFC128jd2D0sgWKCUgKGCHtfR159zfKWcEO9krsLoOnCdTzm1UyD\
DMjkIjqeN/1j8PdMJaRAwV4On079O0DVu6bl1jVtkzo/e/ZmwPr/X436V4xiw/hZt\
w4sfNsSbmsT0+UAQ20X/xaw==:
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"proof": "httpsig",
"key": {
"jwk": {
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"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "RS256",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
}
}
If the HTTP Message includes a message body, the verifier MUST
calculate and verify the value of the "Digest" header. The verifier
MUST ensure that the signature includes all required covered content.
The verifier MUST validate the signature against the expected key of
the signer.
7.3.2. Mutual TLS
This method is indicated by "mtls" in the "proof" field. The signer
presents its TLS client certificate during TLS negotiation with the
verifier.
In this example, the certificate is communicated to the application
through the "Client-Cert" header from a TLS reverse proxy, leading to
the following full HTTP request message:
POST /gnap HTTP/1.1
Host: server.example.com
Content-Type: application/jose
Content-Length: 1567
Client-Cert: \
:MIIC6jCCAdKgAwIBAgIGAXjw74xPMA0GCSqGSIb3DQEBCwUAMDYxNDAyBgNVBAMM\
K05JWU15QmpzRGp5QkM5UDUzN0Q2SVR6a3BEOE50UmppOXlhcEV6QzY2bVEwHhcN\
MjEwNDIwMjAxODU0WhcNMjIwMjE0MjAxODU0WjA2MTQwMgYDVQQDDCtOSVlNeUJq\
c0RqeUJDOVA1MzdENklUemtwRDhOdFJqaTl5YXBFekM2Nm1RMIIBIjANBgkqhkiG\
9w0BAQEFAAOCAQ8AMIIBCgKCAQEAhYOJ+XOKISdMMShn/G4W9m20mT0VWtQBsmBB\
kI2cmRt4Ai8BfYdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8I\
kZ8NMwSrcUIBZGYXjHpwjzvfGvXH/5KJlnR3/uRUp4Z4Ujk2bCaKegDn11V2vxE4\
1hqaPUnhRZxe0jRETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo+\
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uv4BC0bunS0K3bA/3UgVp7zBlQFoFnLTO2uWp/muLEWGl67gBq9MO3brKXfGhi3k\
OzywzwPTuq+cVQDyEN7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQIDAQABMA0GCSqG\
SIb3DQEBCwUAA4IBAQBnYFK0eYHy+hVf2D58usj39lhL5znb/q9G35GBd/XsWfCE\
wHuLOSZSUmG71bZtrOcx0ptle9bp2kKl4HlSTTfbtpuG5onSa3swRNhtKtUy5NH9\
W/FLViKWfoPS3kwoEpC1XqKY6l7evoTCtS+kTQRSrCe4vbNprCAZRxz6z1nEeCgu\
NMk38yTRvx8ihZpVOuU+Ih+dOtVe/ex5IAPYxlQsvtfhsUZqc7IyCcy72WHnRHlU\
fn3pJm0S5270+Yls3Iv6h3oBAP19i906UjiUTNH3g0xMW+V4uLxgyckt4wD4Mlyv\
jnaQ7Z3sR6EsXMocAbXHIAJhwKdtU/fLgdwL5vtx:
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"proof": "jws",
"key": {
"cert": "MIIC6jCCAdKgAwIBAgIGAXjw74xPMA0GCSqGSIb3DQEBCwUAMD\
YxNDAyBgNVBAMMK05JWU15QmpzRGp5QkM5UDUzN0Q2SVR6a3BEOE50UmppOXlhcEV\
6QzY2bVEwHhcNMjEwNDIwMjAxODU0WhcNMjIwMjE0MjAxODU0WjA2MTQwMgYDVQQD\
DCtOSVlNeUJqc0RqeUJDOVA1MzdENklUemtwRDhOdFJqaTl5YXBFekM2Nm1RMIIBI\
jANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAhYOJ+XOKISdMMShn/G4W9m20mT\
0VWtQBsmBBkI2cmRt4Ai8BfYdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8\
KowlyVy8IkZ8NMwSrcUIBZGYXjHpwjzvfGvXH/5KJlnR3/uRUp4Z4Ujk2bCaKegDn\
11V2vxE41hqaPUnhRZxe0jRETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDad\
z8BkPo+uv4BC0bunS0K3bA/3UgVp7zBlQFoFnLTO2uWp/muLEWGl67gBq9MO3brKX\
fGhi3kOzywzwPTuq+cVQDyEN7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQIDAQABMA0\
GCSqGSIb3DQEBCwUAA4IBAQBnYFK0eYHy+hVf2D58usj39lhL5znb/q9G35GBd/Xs\
WfCEwHuLOSZSUmG71bZtrOcx0ptle9bp2kKl4HlSTTfbtpuG5onSa3swRNhtKtUy5\
NH9W/FLViKWfoPS3kwoEpC1XqKY6l7evoTCtS+kTQRSrCe4vbNprCAZRxz6z1nEeC\
guNMk38yTRvx8ihZpVOuU+Ih+dOtVe/ex5IAPYxlQsvtfhsUZqc7IyCcy72WHnRHl\
Ufn3pJm0S5270+Yls3Iv6h3oBAP19i906UjiUTNH3g0xMW+V4uLxgyckt4wD4Mlyv\
jnaQ7Z3sR6EsXMocAbXHIAJhwKdtU/fLgdwL5vtx"
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
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},
"subject": {
"formats": ["iss_sub", "opaque"]
}
}
The verifier compares the TLS client certificate presented during
mutual TLS negotiation to the expected key of the signer. Since the
TLS connection covers the entire message, there are no additional
requirements to check.
Note that in many instances, the verifier will not do a full
certificate chain validation of the presented TLS client certificate,
as the means of trust for this certificate could be in something
other than a PKI system, such as a static registration or trust-on-
first-use.
[[ See issue #110 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/110) ]]
7.3.3. Detached JWS
This method is indicated by "jwsd" in the "proof" field. A JWS
[RFC7515] object is created as follows:
To protect the request, the JOSE header of the signature contains the
following parameters:
kid (string) The key identifier. RECOMMENDED. If the key is
presented in JWK format, this MUST be the value of the "kid" field
of the key.
alg (string) The algorithm used to sign the request. REQUIRED.
MUST be appropriate to the key presented. If the key is presented
as a JWK, this MUST be equal to the "alg" parameter of the key.
MUST NOT be "none".
typ (string) The type header, value "gnap-binding+jwsd". REQUIRED
htm (string) The HTTP Method used to make this request, as an
uppercase ASCII string. REQUIRED
uri (string) The HTTP URI used for this request, including all path
and query components and no fragment component. REQUIRED
created (integer) A timestamp of when the signature was created, in
integer seconds since UNIX Epoch
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ath (string) When a request is bound to an access token, the access
token hash value. The value MUST be the result of Base64url
encoding (with no padding) the SHA-256 digest of the ASCII
encoding of the associated access token's value. REQUIRED if the
request protects an access token.
If the HTTP request has a message body, such as an HTTP POST or PUT
method, the payload of the JWS object is the Base64url encoding
(without padding) of the SHA256 digest of the bytes of the body. If
the request being made does not have a message body, such as an HTTP
GET, OPTIONS, or DELETE method, the JWS signature is calculated over
an empty payload.
The client instance presents the signed object in compact form
[RFC7515] in the Detached-JWS HTTP Header field.
In this example, the JOSE Header contains the following parameters:
{
"alg": "RS256",
"kid": "gnap-rsa",
"uri": "https://server.example.com/gnap",
"htm": "POST",
"typ": "gnap-binding+jwsd",
"created": 1618884475
}
The request body is the following JSON object:
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NOTE: '\' line wrapping per RFC 8792
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"proof": "jwsd",
"key": {
"jwk": {
"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "RS256",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
}
}
This is hashed to the following Base64 encoded value:
PGiVuOZUcN1tRtUS6tx2b4cBgw9mPgXG3IPB3wY7ctc
This leads to the following full HTTP request message:
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NOTE: '\' line wrapping per RFC 8792
POST /gnap HTTP/1.1
Host: server.example.com
Content-Type: application/json
Content-Length: 983
Detached-JWS: eyJhbGciOiJSUzI1NiIsImNyZWF0ZWQiOjE2MTg4ODQ0NzUsImh0b\
SI6IlBPU1QiLCJraWQiOiJnbmFwLXJzYSIsInR5cCI6ImduYXAtYmluZGluZytqd3\
NkIiwidXJpIjoiaHR0cHM6Ly9zZXJ2ZXIuZXhhbXBsZS5jb20vZ25hcCJ9.PGiVuO\
ZUcN1tRtUS6tx2b4cBgw9mPgXG3IPB3wY7ctc.fUq-SV-A1iFN2MwCRW_yolVtT2_\
TZA2h5YeXUoi5F2Q2iToC0Tc4drYFOSHIX68knd68RUA7yHqCVP-ZQEd6aL32H69e\
9zuMiw6O_s4TBKB3vDOvwrhYtDH6fX2hP70cQoO-47OwbqP-ifkrvI3hVgMX9TfjV\
eKNwnhoNnw3vbu7SNKeqJEbbwZfpESaGepS52xNBlDNMYBQQXxM9OqKJaXffzLFEl\
-Xe0UnfolVtBraz3aPrPy1C6a4uT7wLda3PaTOVtgysxzii3oJWpuz0WP5kRujzDF\
wX_EOzW0jsjCSkL-PXaKSpZgEjNjKDMg9irSxUISt1C1T6q3SzRgfuQ
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"proof": "jwsd",
"key": {
"jwk": {
"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "RS256",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
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"name": "My Client Display Name",
"uri": "https://client.foo/"
},
}
}
When the verifier receives the Detached-JWS header, it MUST parse and
validate the JWS object. The signature MUST be validated against the
expected key of the signer. All required fields MUST be present and
their values MUST be valid. If the HTTP message request contains a
body, the verifier MUST calculate the hash of body just as the signer
does, with no normalization or transformation of the request.
7.3.4. Attached JWS
This method is indicated by "jws" in the "proof" field. A JWS
[RFC7515] object is created as follows:
The JOSE header MUST contain the "kid" parameter of the key bound to
this client instance for this request. The "alg" parameter MUST be
set to a value appropriate for the key identified by kid and MUST NOT
be "none".
To protect the request, the JWS header MUST contain the following
additional parameters.
typ (string) The type header, value "gnap-binding+jws".
htm (string) The HTTP Method used to make this request, as an
uppercase ASCII string.
uri (string) The HTTP URI used for this request, including all path
and query components and no fragment component.
created (integer) A timestamp of when the signature was created, in
integer seconds since UNIX Epoch
ath (string) When a request is bound to an access token, the access
token hash value. The value MUST be the result of Base64url
encoding (with no padding) the SHA-256 digest of the ASCII
encoding of the associated access token's value.
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If the HTTP request has a message body, such as an HTTP POST or PUT
method, the payload of the JWS object is the JSON serialized body of
the request, and the object is signed according to JWS and serialized
into compact form [RFC7515]. The client instance presents the JWS as
the body of the request along with a content type of "application/
jose". The AS MUST extract the payload of the JWS and treat it as
the request body for further processing.
If the request being made does not have a message body, such as an
HTTP GET, OPTIONS, or DELETE method, the JWS signature is calculated
over an empty payload and passed in the "Detached-JWS" header as
described in Section 7.3.3.
In this example, the JOSE header contains the following parameters:
{
"alg": "RS256",
"kid": "gnap-rsa",
"uri": "https://server.example.com/gnap",
"htm": "POST",
"typ": "gnap-binding+jwsd",
"created": 1618884475
}
The request body, used as the JWS Payload, is the following JSON
object:
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NOTE: '\' line wrapping per RFC 8792
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"proof": "jws",
"key": {
"jwk": {
"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "RS256",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
},
"subject": {
"formats": ["iss_sub", "opaque"]
}
}
This leads to the following full HTTP request message:
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NOTE: '\' line wrapping per RFC 8792
POST /gnap HTTP/1.1
Host: server.example.com
Content-Type: application/jose
Content-Length: 1047
eyJhbGciOiJSUzI1NiIsImNyZWF0ZWQiOjE2MTg4ODQ0NzUsImh0bSI6IlBPU1QiLCJ\
raWQiOiJnbmFwLXJzYSIsInR5cCI6ImduYXAtYmluZGluZytqd3NkIiwidXJpIjoiaH\
R0cHM6Ly9zZXJ2ZXIuZXhhbXBsZS5jb20vZ25hcCJ9.CnsKICAgICJhY2Nlc3NfdG9r\
ZW4iOiB7CiAgICAgICAgImFjY2VzcyI6IFsKICAgICAgICAgICAgImRvbHBoaW4tbWV\
0YWRhdGEiCiAgICAgICAgXQogICAgfSwKICAgICJpbnRlcmFjdCI6IHsKICAgICAgIC\
Aic3RhcnQiOiBbInJlZGlyZWN0Il0sCiAgICAgICAgImZpbmlzaCI6IHsKICAgICAgI\
CAgICAgIm1ldGhvZCI6ICJyZWRpcmVjdCIsCiAgICAgICAgICAgICJ1cmkiOiAiaHR0\
cHM6Ly9jbGllbnQuZm9vL2NhbGxiYWNrIiwKICAgICAgICAgICAgIm5vbmNlIjogIlZ\
KTE82QTRDQVlMQlhIVFIwS1JPIgogICAgICAgIH0KICAgIH0sCiAgICAiY2xpZW50Ij\
ogewogICAgICAicHJvb2YiOiAiandzIiwKICAgICAgImtleSI6IHsKICAgICAgICAia\
ndrIjogewogICAgICAgICAgICAia2lkIjogImduYXAtcnNhIiwKICAgICAgICAgICAg\
Imt0eSI6ICJSU0EiLAogICAgICAgICAgICAiZSI6ICJBUUFCIiwKICAgICAgICAgICA\
gImFsZyI6ICJSUzI1NiIsCiAgICAgICAgICAgICJuIjogImhZT0otWE9LSVNkTU1TaG\
5fRzRXOW0yMG1UMFZXdFFCc21CQmtJMmNtUnQ0QWk4QmZZZEhzRnpBdFlLT2pwQlIxU\
nBLcEptVkt4SUdOeTBnNlozYWQyWFlzaDhLb3dseVZ5OElrWjhOTXdTcmNVSUJaR1lY\
akhwd2p6dmZHdlhIXzVLSmxuUjNfdVJVcDRaNFVqazJiQ2FLZWdEbjExVjJ2eEU0MWh\
xYVBVbmhSWnhlMGpSRVRkZHpzRTNtdTFTSzhkVENST2p3VWwxNG1VTm84aVRyVG00bj\
BxRGFkejhCa1BvLXV2NEJDMGJ1blMwSzNiQV8zVWdWcDd6QmxRRm9GbkxUTzJ1V3Bfb\
XVMRVdHbDY3Z0JxOU1PM2JyS1hmR2hpM2tPenl3endQVHVxLWNWUUR5RU43YUwwU3hD\
YjNIYzRJZHFEYU1nOHFIVXlPYnBQaXREUSIKICAgICAgICB9CiAgICAgIH0KICAgICA\
gImRpc3BsYXkiOiB7CiAgICAgICAgIm5hbWUiOiAiTXkgQ2xpZW50IERpc3BsYXkgTm\
FtZSIsCiAgICAgICAgInVyaSI6ICJodHRwczovL2NsaWVudC5mb28vIgogICAgICB9L\
AogICAgfSwKICAgICJzdWJqZWN0IjogewogICAgICAgICJmb3JtYXRzIjogWyJpc3Nf\
c3ViIiwgIm9wYXF1ZSJdCiAgICB9Cn0K.MwNoVMQp5hVxI0mCs9LlOUdFtkDXaA1_eT\
vOXq7DOGrtDKH7q4vP2xUq3fH2jRAZqnobo0WdPP3eM3NH5QUjW8pa6_QpwdIWkK7r-\
u_52puE0lPBp7J4U2w4l9gIbg8iknsmWmXeY5F6wiGT8ptfuEYGgmloAJd9LIeNvD3U\
LW2h2dz1Pn2eDnbyvgB0Ugae0BoZB4f69fKWj8Z9wvTIjk1LZJN1PcL7_zT8Lrlic9a\
PyzT7Q9ovkd1s-4whE7TrnGUzFc5mgWUn_gsOpsP5mIIljoEEv-FqOW2RyNYulOZl0Q\
8EnnDHV_vPzrHlUarbGg4YffgtwkQhdK72-JOxYQ
[[ See issue #109 (https://github.com/ietf-wg-gnap/gnap-core-
protocol/issues/109) ]]
When the verifier receives an attached JWS request, it MUST parse and
validate the JWS object. The signature MUST be validated against the
expected key of the signer. All required fields MUST be present and
their values MUST be valid. If the HTTP message request contains a
body, the verifier MUST decode the payload of the JWS object and
treat this as the HTTP message body.
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8. Resource Access Rights
GNAP provides a rich structure for describing the protected resources
hosted by RSs and accessed by client software. This structure is
used when the client instance requests an access token (Section 2.1)
and when an access token is returned (Section 3.2).
The root of this structure is a JSON array. The elements of the JSON
array represent rights of access that are associated with the the
access token. The resulting access is the union of all elements
within the array.
The access associated with the access token is described using
objects that each contain multiple dimensions of access. Each object
contains a REQUIRED "type" property that determines the type of API
that the token is used for.
type (string) The type of resource request as a string. This field
MAY define which other fields are allowed in the request object.
This field is REQUIRED.
The value of the "type" field is under the control of the AS. This
field MUST be compared using an exact byte match of the string value
against known types by the AS. The AS MUST ensure that there is no
collision between different authorization data types that it
supports. The AS MUST NOT do any collation or normalization of data
types during comparison. It is RECOMMENDED that designers of
general-purpose APIs use a URI for this field to avoid collisions
between multiple API types protected by a single AS.
While it is expected that many APIs will have their own properties, a
set of common properties are defined here. Specific API
implementations SHOULD NOT re-use these fields with different
semantics or syntax. The available values for these properties are
determined by the API being protected at the RS.
actions (array of strings) The types of actions the client instance
will take at the RS as an array of strings. For example, a client
instance asking for a combination of "read" and "write" access.
locations (array of strings) The location of the RS as an array of
strings. These strings are typically URIs identifying the
location of the RS.
datatypes (array of strings) The kinds of data available to the
client instance at the RS's API as an array of strings. For
example, a client instance asking for access to raw "image" data
and "metadata" at a photograph API.
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identifier (string) A string identifier indicating a specific
resource at the RS. For example, a patient identifier for a
medical API or a bank account number for a financial API.
privileges (array of strings) The types or levels of privilege being
requested at the resource. For example, a client instance asking
for administrative level access, or access when the resource owner
is no longer online.
The following non-normative example is describing three kinds of
access (read, write, delete) to each of two different locations and
two different data types (metadata, images) for a single access token
using the fictitious "photo-api" type definition.
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"delete"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
}
]
The access requested for a given object when using these fields is
the cross-product of all fields of the object. That is to say, the
object represents a request for all "actions" listed to be used at
all "locations" listed for all possible "datatypes" listed within the
object. Assuming the request above was granted, the client instance
could assume that it would be able to do a "read" action against the
"images" on the first server as well as a "delete" action on the
"metadata" of the second server, or any other combination of these
fields, using the same access token.
To request a different combination of access, such as requesting one
of the possible "actions" against one of the possible "locations" and
a different choice of possible "actions" against a different one of
the possible "locations", the client instance can include multiple
separate objects in the "resources" array. The following non-
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normative example uses the same fictitious "photo-api" type
definition to request a single access token with more specifically
targeted access rights by using two discrete objects within the
request.
"access": [
{
"type": "photo-api",
"actions": [
"read"
],
"locations": [
"https://server.example.net/"
],
"datatypes": [
"images"
]
},
{
"type": "photo-api",
"actions": [
"write",
"delete"
],
"locations": [
"https://resource.local/other"
],
"datatypes": [
"metadata"
]
}
]
The access requested here is for "read" access to "images" on one
server while simultaneously requesting "write" and "delete" access
for "metadata" on a different server, but importantly without
requesting "write" or "delete" access to "images" on the first
server.
It is anticipated that API designers will use a combination of common
fields defined in this specification as well as fields specific to
the API itself. The following non-normative example shows the use of
both common and API-specific fields as part of two different
fictitious API "type" values. The first access request includes the
"actions", "locations", and "datatypes" fields specified here as well
as the API-specific "geolocation" field. The second access request
includes the "actions" and "identifier" fields specified here as well
as the API-specific "currency" field.
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"access": [
{
"type": "photo-api",
"actions": [
"read",
"write"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
],
"geolocation": [
{ lat: -32.364, lng: 153.207 },
{ lat: -35.364, lng: 158.207 }
]
},
{
"type": "financial-transaction",
"actions": [
"withdraw"
],
"identifier": "account-14-32-32-3",
"currency": "USD"
}
]
If this request is approved, the resulting access token
(Section 3.2.1)'s access rights will be the union of the requested
types of access for each of the two APIs, just as above.
8.1. Requesting Resources By Reference
Instead of sending an object describing the requested resource
(Section 8), access rights MAY be communicated as a string known to
the AS or RS representing the access being requested. Each string
SHOULD correspond to a specific expanded object representation at the
AS.
"access": [
"read", "dolphin-metadata", "some other thing"
]
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This value is opaque to the client instance and MAY be any valid JSON
string, and therefore could include spaces, unicode characters, and
properly escaped string sequences. However, in some situations the
value is intended to be seen and understood by the client software's
developer. In such cases, the API designer choosing any such human-
readable strings SHOULD take steps to ensure the string values are
not easily confused by a developer, such as by limiting the strings
to easily disambiguated characters.
This functionality is similar in practice to OAuth 2.0's "scope"
parameter [RFC6749], where a single string represents the set of
access rights requested by the client instance. As such, the
reference string could contain any valid OAuth 2.0 scope value as in
Appendix D.5. Note that the reference string here is not bound to
the same character restrictions as in OAuth 2.0's "scope" definition.
A single "access" array MAY include both object-type and string-type
resource items. In this non-normative example, the client instance
is requesting access to a "photo-api" and "financial-transaction" API
type as well as the reference values of "read", "dolphin-metadata",
and "some other thing".
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"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"delete"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read",
"dolphin-metadata",
{
"type": "financial-transaction",
"actions": [
"withdraw"
],
"identifier": "account-14-32-32-3",
"currency": "USD"
},
"some other thing"
]
The requested access is the union of all elements of the array,
including both objects and reference strings.
9. Discovery
By design, the protocol minimizes the need for any pre-flight
discovery. To begin a request, the client instance only needs to
know the endpoint of the AS and which keys it will use to sign the
request. Everything else can be negotiated dynamically in the course
of the protocol.
However, the AS can have limits on its allowed functionality. If the
client instance wants to optimize its calls to the AS before making a
request, it MAY send an HTTP OPTIONS request to the grant request
endpoint to retrieve the server's discovery information. The AS MUST
respond with a JSON document containing the following information:
grant_request_endpoint (string) REQUIRED. The location of the AS's
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grant request endpoint. The location MUST be a URL [RFC3986] with
a scheme component that MUST be https, a host component, and
optionally, port, path and query components and no fragment
components. This URL MUST match the URL the client instance used
to make the discovery request.
interaction_start_modes_supported (array of strings) OPTIONAL. A
list of the AS's interaction start methods. The values of this
list correspond to the possible values for the interaction start
section (Section 2.5.1) of the request.
interaction_finish_methods_supported (array of strings) OPTIONAL. A
list of the AS's interaction finish methods. The values of this
list correspond to the possible values for the method element of
the interaction finish section (Section 2.5.2) of the request.
key_proofs_supported (array of strings) OPTIONAL. A list of the
AS's supported key proofing mechanisms. The values of this list
correspond to possible values of the "proof" field of the key
section (Section 7.1) of the request.
subject_formats_supported (array of strings) OPTIONAL. A list of
the AS's supported subject identifier types. The values of this
list correspond to possible values of the subject identifier
section (Section 2.2) of the request.
assertions_supported (array of strings) OPTIONAL. A list of the
AS's supported assertion formats. The values of this list
correspond to possible values of the subject assertion section
(Section 2.2) of the request.
The information returned from this method is for optimization
purposes only. The AS MAY deny any request, or any portion of a
request, even if it lists a capability as supported. For example, a
given client instance can be registered with the "mtls" key proofing
mechanism, but the AS also returns other proofing methods, then the
AS will deny a request from that client instance using a different
proofing mechanism.
9.1. RS-first Method of AS Discovery
If the client instance calls an RS without an access token, or with
an invalid access token, the RS MAY respond to the client instance
with an authentication header indicating that GNAP needs to be used
to access the resource. The address of the GNAP endpoint MUST be
sent in the "as_uri" parameter. The RS MAY additionally return a
resource reference that the client instance MAY use in its access
token request. This resource reference MUST be sufficient for at
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least the action the client instance was attempting to take at the RS
and MAY be more powerful. The means for the RS to determine the
resource reference are out of scope of this specification, but some
dynamic methods are discussed in
[I-D.draft-ietf-gnap-resource-servers]. The content of the resource
reference is opaque to the client instance.
NOTE: '\' line wrapping per RFC 8792
WWW-Authenticate: \
GNAP as_uri=https://server.example/tx,access=FWWIKYBQ6U56NL1
The client instance then makes a request to the "as_uri" as described
in Section 2, with the value of "access" as one of the members of the
"access" array in the "access_token" portion of the request. The
client instance MAY request additional resources and other
information. The client instance MAY request multiple access tokens.
In this non-normative example, the client instance is requesting a
single access token using the resource reference "FWWIKYBQ6U56NL1"
received from the RS in addition to the "dolphin-metadata" resource
reference that the client instance has been configured with out of
band.
POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": {
"access": [
"FWWIKYBQ6U56NL1",
"dolphin-metadata"
]
},
"client": "KHRS6X63AJ7C7C4AZ9AO"
}
If issued, the resulting access token would contain sufficient access
to be used at both referenced resources.
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10. Acknowledgements
The editors would like to thank the feedback of the following
individuals for their reviews, implementations, and contributions:
Aeke Axeland, Aaron Parecki, Adam Omar Oueidat, Annabelle Backman,
Dick Hardt, Dmitri Zagidulin, Dmitry Barinov, Fabien Imbault, Francis
Pouatcha, George Fletcher, Haardik Haardik, Hamid Massaoud, Jacky
Yuan, Joseph Heenan, Justin Richer, Kathleen Moriarty, Mike Jones,
Mike Varley, Nat Sakimura, Takahiko Kawasaki, Takahiro Tsuchiya.
The editors would also like to thank the GNAP working group design
team of Kathleen Moriarty, Fabien Imbault, Dick Hardt, Mike Jones,
and Justin Richer, who incorporated elements from the XAuth and XYZ
proposals to create the first version of this document.
In addition, the editors would like to thank Aaron Parecki and Mike
Jones for insights into how to integrate identity and authentication
systems into the core protocol, and Justin Richer and Dick Hardt for
the use cases, diagrams, and insights provided in the XYZ and XAuth
proposals that have been incorporated here. The editors would like
to especially thank Mike Varley and the team at SecureKey for
feedback and development of early versions of the XYZ protocol that
fed into this standards work.
11. IANA Considerations
[[ TBD: There are a lot of items in the document that are expandable
through the use of value registries. ]]
12. Security Considerations
12.1. TLS Protection in Transit
All requests in GNAP have to be made over TLS or equivalent as
outlined in [BCP195] to protect the contents of the request and
response from manipulation and interception by an attacker. This
includes all requests from a client instance to the AS, all requests
from the client instance to an RS, any requests back to a client
instance such as the push-based interaction finish method, and any
back-end communications such as from an RS to an AS as described in
[I-D.draft-ietf-gnap-resource-servers]. Additionally, all requests
between a browser and other components, such as during redirect-based
interaction, need to be made over TLS or use equivalent protection.
Even though requests from the client instance to the AS are signed,
the signature method alone does not protect the request from
interception by an attacker. TLS protects the response as well as
the request, preventing an attacker from intercepting requested
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information as it is returned. This is particularly important in the
core protocol for security artifacts such as nonces and for personal
information such as subject information.
The use of key-bound access tokens does not negate the requirement
for protecting calls to the RS with TLS. While the keys and
signatures associated a bound access token will prevent an attacker
from using a stolen token, without TLS an attacker would be able to
watch the data being sent to the RS and returned from the RS during
legitimate use of the client instance under attack. Additionally,
without TLS an attacker would be able to profile the calls made
between the client instance and RS, possibly gaining information
about the functioning of the API between the client software and RS
software that would be otherwise unknown to the attacker.
TLS or equivalent protection also needs to be used between the
browser and any other components. This applies during initial
redirects to an AS's components during interaction, during any
interaction with the resource owner, and during any redirect back to
the client instance. Without TLS protection on these portions of the
process, an attacker could wait for a valid request to start and then
take over the resource owner's interaction session.
12.2. Protection of Client Instance Key Material
Client instances are identified by their unique keys, and anyone with
access to a client instance's key material will be able to
impersonate that client instance to all parties. This is true for
both calls to the AS as well as calls to an RS using a key-bound
access token.
Different types of client software have different methods available
for creating, managing, and registering keys. GNAP explicitly allows
for ephemeral clients, such as SPAs, and single-user clients, such as
mobile applications, to create and present their own keys during the
initial grant request. The client software can securely generate a
keypair on-device and present the public key, along with proof of
holding that public key, to the AS as part of the initial request.
To facilitate trust in these ephemeral keys, GNAP further allows for
an extensible set of client information to be passed with the
request. This information can include device posture and third-party
attestations of the client software's provenance and authenticity,
depending on the needs and capabilities of the client software and
its deployment.
From GNAP's perspective, each distinct key is a different client
instance. However, multiple client instances can be grouped together
by an AS policy and treated similarly to each other. For instance,
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if an AS knows of several different keys for different servers within
a cluster, the AS can decide that authorization of one of these
servers applies to all other servers within the cluster. An AS that
chooses to do this needs to be careful with how it groups different
client keys together in its policy, since the breach of one instance
would have direct effects on the others in the cluster.
Additionally, if an end user controls multiple instances of a single
type of client software, such as having an application installed on
multiple devices, each of these instances is expected to have a
separate key and be issued separate access tokens. However, if the
AS is able to group these separate instances together as described
above, it can streamline the authorization process for new instances
of the same client software. For example, if two client instances
can present proof of a valid installation of a piece of client
software, the AS would be able to associate the approval of the first
instance of this software to all related instances. The AS could
then choose to bypass an explicit prompt of the resource owner for
approval during authorization, since such approval has already been
given. An AS doing such a process would need to take assurance
measures that the different instances are in fact correlated and
authentic, as well as ensuring the expected resource owner is in
control of the client instance.
Finally, if multiple instances of client software each have the same
key, then from GNAP's perspective, these are functionally the same
client instance as GNAP has no reasonable way to differentiate
between them. This situation could happen if multiple instances
within a cluster can securely share secret information among
themselves. Even though there are multiple copies of the software,
the shared key makes these copies all present as a single instance.
It is considered bad practice to share keys between copies of
software unless they are very tightly integrated with each other and
can be closely managed. It is particularly bad practice to allow an
end-user to copy keys between client instances and to willingly use
the same key in multiple instances.
12.3. Protection of Authorization Server
The AS performs critical functions in GNAP, including authenticating
client software, managing interactions with end-users to gather
consent and provide notice, and issuing access tokens for client
instances to present to resource servers. As such, protecting the AS
is central to any GNAP deployment.
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If an attacker is able to gain control over an AS, they would be able
to create fraudulent tokens and manipulate registration information
to allow for malicious clients. These tokens and clients would be
trusted by other components in the ecosystem under the protection of
the AS.
If the AS is using signed access tokens, an attacker in control of
the AS's signing keys would be able to manufacture fraudulent tokens
for use at RS's under the protection of the AS.
If an attacker is able to impersonate an AS, they would be able to
trick legitimate client instances into making signed requests for
information which could potentially be proxied to a real AS. To
combat this, all communications to the AS need to be made over TLS or
its equivalent, and the software making the connection has to
validate the certificate chain of the host it is connecting to.
Consequently, protecting, monitoring, and auditing the AS is
paramount to preserving the security of a GNAP-protected ecosystem.
12.4. Symmetric and Asymmetric Client Instance Keys
The cryptographic methods used by GNAP for key-proofing can support
both asymmetric and symmetric cryptography, and can be extended to
use a wide variety of mechanisms. While symmetric cryptographic
systems have some benefits in speed and simplicity, they have a
distinct drawback that both parties need access to the same key in
order to do both signing and verification of the message. This means
that when the client instance calls the AS to request a token, the AS
needs to know the exact value of the client instance's key (or be
able to derive it) in order to validate the key proof signature.
With asymmetric keys, the client needs only to send its public key to
the AS to allow for verification that the client holds the associated
private key, regardless of whether that key was pre-registered or not
with the AS.
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When used to bind to an access token, a key value must be known by
the RS in order to validate the proof signature on the request.
Common methods for communicating these proofing keys include putting
information in a structured access token and allowing the RS to look
up the associated key material against the value of the access token.
With symmetric cryptography, both of these methods would expose the
signing key to the RS, and in the case of an structured access token,
potentially to any party that can see the access token itself unless
the token's payload has been encrypted. Any of these parties would
then be able to make calls using the access token by creating a valid
signature. With asymmetric cryptography, the RS only needs to know
the public key associated with the token in order to validate, and
therefore cannot create any new calls.
Symmetric keys also have the expected advantage of providing better
protection against quantum threats in the future. Also, these types
of keys (and their secure derivations) are widely supported among
many cloud-based key management systems.
While both signing approaches are allowed, GNAP treats these two
classes of keys somewhat differently. Only the public portion of
asymmetric keys are allowed to be sent by value in requests to the AS
when establishing a connection. Since sending a symmetric key (or
the private portion of an asymmetric key) would expose the signing
material to any parties on the request path, including any attackers,
sending these kinds of keys is prohibited. Symmetric keys can still
be used by client instances, but only a reference to the key and not
its value can be sent. This allows the AS to use pre-registered
symmetric keys as well as key derivation schemes to take advantage of
symmetric cryptography but without requiring key distribution at
runtime, which would expose the keys in transit.
Both the AS and client software can use systems such as hardware
security modules to strengthen their key security storage and
generation for both asymmetric and symmetric keys.
12.5. Generation of Access Tokens
The content of access tokens need to be such that only the generating
AS would be able to create them, and the contents cannot be
manipulated by an attacker to gain different or additional access
rights.
One method for accomplishing this is to use a cryptographically
random value for the access token, generated by the AS using a secure
randomization function with sufficiently high entropy. The odds of
an attacker guessing the output of the randomization function to
collide with a valid access token are exceedingly small, and even
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then the attacker would not have any control over what the access
token would represent since that information would be held close by
the AS.
Another method for accomplishing this is to use a structured token
that is cryptographically signed. In this case, the payload of the
access token declares to the RS what the token is good for, but the
signature applied by the AS during token generation covers this
payload. Only the AS can create such a signature and therefore only
the AS can create such a signed token. The odds of an attacker being
able to guess a signature value with a useful payload are exceedingly
small. This technique only works if all targeted RS's check the
signature of the access token. Any RS that does not validate the
signature of all presented tokens would be susceptible to injection
of a modified or falsified token. Furthermore, an AS has to
carefully protect the keys used to sign access tokens, since anyone
with access to these signing keys would be able to create seemingly-
valid access tokens using them.
12.6. Bearer Access Tokens
Bearer access tokens can be used by any party that has access to the
token itself, without any additional information. As a natural
consequence, any RS that a bearer token is presented to has the
technical capability of presenting that bearer token to another RS,
as long as the token is valid. It also means that any party that is
able capture of the token value in storage or in transit is able to
use the access token. While bearer tokens are inherently simpler,
this simplicity has been misapplied and abused in making needlessly
insecure systems.
In GNAP, key-bound access tokens are the default due to their higher
security properties. While bearer tokens can be used in GNAP, their
use should be limited onto to cases where the simplicity benefits
outweigh the significant security downsides.
12.7. Key-Bound Token Access Tokens
Key-bound access tokens, as the name suggests, are bound to a
specific key and must be presented along with proof of that key
during use. The key itself is not presented at the same time as the
token, so even if a token value is captured, it cannot be used to
make a new request. This is particularly true for an RS, which will
see the token value but will not see the keys used to make the
request.
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Key-bound access tokens provide this additional layer of protection
only when the RS checks the signature of the message presented with
the token. Acceptance of an invalid presentation signature, or
failure to check the signature entirely, would allow an attacker to
make calls with a captured access token without having access to the
related signing key material.
In addition to validating the signature of the presentation message
itself, the RS also needs to ensure that the signing key used is
appropriate for the presented token. If an RS does not ensure that
the right keys were used to sign a message with a specific token, an
attacker would be able to capture an access token and sign the
request with their own keys, thereby negating the benefits of using
key-bound access tokens.
The RS also needs to ensure that a sufficient portions of the message
are covered by the signature. Any items outside the signature could
still affect the API's processing decisions, but these items would
not be strongly bound to the token presentation. As such, an
attacker could capture a valid request, then manipulate portions of
the request outside of the signature envelope in order to cause
unwanted actions at the protected API.
Some key-bound tokens are susceptible to replay attacks, depending on
the details of the signing method used. If a signature method covers
only portions of a given request, that same signature proof can be
used by an attacker to make a similar call, potentially even varying
elements that are outside of the protection of the signature. Key
proofing mechanisms used with access tokens therefore need to use
replay protection mechanisms covered under the signature such as a
per-message nonce, a reasonably short time validity window, or other
uniqueness constraints. The details of using these will vary
depending on the key proofing mechanism in use, but for example, HTTP
Message Signatures has both a "created" and "nonce" signature
parameter as well as the ability to cover significant portions of the
HTTP message.
12.8. Exposure of End-user Credentials to Client Instance
As a delegation protocol, one of the main goals of GNAP is to prevent
the client software from being exposed to any credentials or
information about the end-user or resource owner as a requirement of
the delegation process. By using the variety of interaction
mechanisms, the resource owner can interact with the AS without ever
authenticating to the client software, and without the client
software having to impersonate the resource owner through replay of
their credentials.
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Consequently, no interaction methods defined in the GNAP core require
the end-user to enter their credentials, but it is technologically
possible for an extension to be defined to carry such values. Such
an extension would be dangerous as it would allow rogue client
software to directly collect, store, and replay the end-user's
credentials outside of any legitimate use within a GNAP request.
The concerns of such an extension could be mitigated through use of a
challenge and response unlocked by the end user's credentials. For
example, the AS presents a challenge as part of an interaction start
method, and the client instance signs that challenge using a key
derived from a password presented by the end user. It would be
possible for the client software to collect this password in a secure
software enclave without exposing the password to the rest of the
client software or putting it across the wire to the AS. The AS can
validate this challenge response against a known password for the
identified end user. While an approach such as this does not remove
all of the concerns surrounding such a password-based scheme, it is
at least possible to implement in a more secure fashion than simply
collecting and replaying the password. Even so, such schemes should
only ever be used by trusted clients due to the ease of abusing them.
12.9. Mixing Up Authorization Servers
If a client instance is able to work with multiple AS's
simultaneously, it is more possible for an attacker to add a
compromised AS to the client instance's configuration and cause the
client software to start a request at the compromised AS. This AS
could then proxy the client's request to a valid AS in order to
attempt to get the resource owner to approve access for the
legitimate client instance.
A client instance needs to always be aware of which AS it is talking
to throughout a grant process, and ensure that any callback for one
AS does not get conflated with the callback to different AS. The
interaction finish hash calculate allows a client instance to protect
against this kind of substitution, but only if the client instance
validates the hash. If the client instance does not use an
interaction finish method or does not check the interaction finish
hash value, the compromised AS can be granted a valid access token on
behalf of the resource owner. See [attack-surfaces] for details of
one such attack, which has been since addressed in this document by
including the grant endpoint in the interaction hash calculation.
The client instance still needs to validate the hash for the attack
to be prevented.
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12.10. Processing of Client-Presented User Information
GNAP allows the client instance to present assertions and identifiers
of the current user to the AS as part of the initial request. This
information should only ever be taken by the AS as a hint, since the
AS has no way to tell if the represented person is present at the
client software, without using an interaction mechanism. This
information does not guarantee the given user is there, but it does
constitute a statement by the client software that the AS can take
into account.
For example, if a specific user is claimed to be present prior to
interaction, but a different user is shown to be present during
interaction, the AS can either determine this to be an error or
signal to the client instance through returned subject information
that the current user has changed from what the client instance
thought. This user information can also be used by the AS to
streamline the interaction process when the user is present. For
example, instead of having the user type in their account identifier
during interaction at a redirected URL, the AS can immediately
challenge the user for their account credentials. Alternatively, if
an existing session is detected, the AS can determine that it matches
the identifier provided by the client and subsequently skip an
explicit authentication event by the resource owner.
In cases where the AS trusts the client software more completely, due
to policy or by previous approval of a given client instance, the AS
can take this user information as a statement that the user is
present and could issue access tokens and release subject information
without interaction. The AS should only take such action in very
limited circumstances, as a client instance could assert whatever it
likes for the user's identifiers in its request.
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When a client instance presents an assertion to the AS, the AS needs
to evaluate that assertion. Since the AS is unlikely to be the
intended audience of an assertion held by the client software, the AS
will need to evaluate the assertion in a different context. Even in
this case, the AS can still evaluate that the assertion was generated
by a trusted party, was appropriately signed, and is within any time
validity windows stated by the assertion. If the client instance's
audience identifier is known to the AS and can be associated with the
client instance's presented key, the AS can also evaluate that the
appropriate client instance is presenting the claimed assertion. All
of this will prevent an attacker from presenting a manufactured
assertion, or one captured from an untrusted system. However,
without validating the audience of the assertion, a captured
assertion could be presented by the client instance to impersonate a
given end user. In such cases, the assertion offers little more
protection than a simple identifier would.
A special case exists where the AS is the generator of the assertion
being presented by the client instance. In these cases, the AS can
validate that it did issue the assertion and it is associated with
the client instance presenting the assertion.
12.11. Client Instance Pre-registration
Each client instance is identified by its own unique key, and for
some kinds of client software such as a web server or backend system,
this identification can be facilitated by registering a single key
for a piece of client software ahead of time. This registration can
be associated with a set of display attributes to be used during the
authorization process, identifying the client software to the user.
In these cases, it can be assumed that only one instance of client
software will exist, likely to serve many different users.
A client's registration record needs to include its identifying key.
Furthermore, it is the case that any clients using symmetric
cryptography for key proofing mechanisms need to have their keys pre-
registered. The registration should also include any information
that would aid in the authorization process, such as a display name
and logo. The registration record can also limit a given client to
ask for certain kinds of information and access, or be limited to
specific interaction mechanisms at runtime.
It also is sensible to pre-register client instances when the
software is acting on its own behalf, without the need for a runtime
approval by a resource owner or any interaction with an end-user. In
these cases, an AS needs to rest on the trust decisions that have
been determined prior to runtime in determining what rights and
tokens to grant to a given client instance.
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However, it does not make sense to pre-register many types of
clients. Single-page applications (SPAs) and mobile/desktop
applications in particular present problems with pre-registration.
For SPAs, the instances are ephemeral in nature and long-term
registration of a single instance leads to significant storage and
management overhead at the AS. For mobile applications, each
installation of the client software is a separate instance, and
sharing a key among all instances would be detrimental to security as
the compromise of any single installation would compromise all copies
for all users.
An AS can treat these classes of client software differently from
each other, perhaps by allowing access to certain high-value APIs
only to pre-registered known clients, or by requiring an active end-
user delegation of authority to any client software not pre-
registered.
An AS can also provide warnings and caveats to resource owners during
the authorization process, allowing the user to make an informed
decision regarding the software they are authorizing. For example,
if the AS has done vetting of the client software and this specific
instance, it can present a different authorization screen compared to
a client instance that is presenting all of its information at
runtime.
12.12. Client Instance Impersonation
If client instances are allowed to set their own user-facing display
information, such as a display name and website URL, a malicious
client instance could impersonate legitimate client software for the
purposes of tricking users into authorizing the malicious client.
Requiring clients to pre-register does not fully mitigate this
problem since many pre-registration systems have self-service portals
for management of client registration, allowing authenticated
developers to enter self-asserted information into the management
portal.
An AS can mitigate this by actively filtering all self-asserted
values presented by client software, both dynamically as part of GNAP
and through a registration portal, to limit the kinds of
impersonation that would be done.
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An AS can also warn the resource owner about the provenance of the
information it is displaying, allowing the resource owner to make a
more informed delegation decision. For example, an AS can visually
differentiate between a client instance that can be traced back to a
specific developer's registration and an instance that has self-
asserted its own key and display information.
12.13. Interception of Information in the Browser
Most information passed through the web-browser is susceptible to
interception and possible manipulation by elements within the browser
such as scripts loaded within pages. Information in the URL is
exposed through browser and server logs, and can also leak to other
parties through HTTP "Referrer" headers.
GNAP's design limits the information passed directly through the
browser, allowing for opaque URLs in most circumstances. For the
redirect-based interaction finish mechanism, named query parameters
are used to carry unguessable opaque values. For these, GNAP
requires creation and validation of a cryptographic hash to protect
the query parameters added to the URL and associate them with an
ongoing grant process. The client instance has to properly validate
this hash to prevent an attacker from injecting an interaction
reference intended for a different AS or client instance.
Several interaction start mechanisms use URLs created by the AS and
passed to the client instance. While these URLs are opaque to the
client instance, it's possible for the AS to include parameters,
paths, and other pieces of information that could leak security data
or be manipulated by a party in the middle of the transaction.
12.14. Callback URL Manipulation
The callback URL used in interaction finish mechanisms is defined by
the client instance. This URL is opaque to the AS, but can contain
information relevant to the client instance's operations. In
particular, the client instance can include state information to
allow the callback request to be associated with an ongoing grant
request.
Since this URL is exposed to the end-user's browser, it is
susceptible to both logging and manipulation in transit before the
request is made to the client software. As such, a client instance
should never put security-critical or private information into the
callback URL in a cleartext form. For example, if the client
software includes a post-redirect target URL in its callback URL to
the AS, this target URL could be manipulated by an attacker, creating
an open redirector at the client. Instead, a client instance can use
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an unguessable identifier into the URL that can then be used by the
client software to look up the details of the pending request. Since
this approach requires some form of statefulness by the client
software during the redirection process, clients that are not capable
of holding state through a redirect should not use redirect-based
interaction mechanisms.
12.15. MTLS Deployment Patterns
GNAP does not specify how a client instance's keys could be made
known to the AS ahead of time. Public Key Infrastructure (PKI) can
be used to manage the keys used by client instances when calling the
AS, allowing the AS to trust a root key from a trusted authority.
This method is particularly relevant to the MTLS signature method,
where the client instance presents its certificate to the AS as part
of the TLS connection. An AS using PKI to validate the MTLS
connection would need to ensure that the presented certificate was
issued by a trusted certificate authority before allowing the
connection to continue. PKI-based certificates would allow a key to
be revoked and rotated through management at the certificate
authority without requiring additional registration or management at
the AS. PKI has historically been difficult to deploy, especially at
scale, but it remains an appropriate solution for systems where the
required overhead is not an impediment.
MTLS need not use a PKI backing, as self-signed certificates and
certificates from untrusted authorities can still be presented as
part of a TLS connection. In this case, the AS or RS would validate
the connection but accept whatever certificate was presented by the
client software. This specific certificate would then be bound to
all future connections from that client software by being bound to
the resulting access tokens.
12.16. Interception of Responses from the AS
Responses from the AS contain information vital to both the security
and privacy operations of GNAP. This information includes nonces
used in cryptographic calculations, subject identifiers, assertions,
public keys, and information about what client software is requesting
and was granted.
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In addition, if bearer tokens are used or keys are issued alongside a
bound access token, the response from the AS contains all information
necessary for use of the contained access token. Any party that is
capable of viewing such a response, such as an intermediary proxy,
would be able to exfiltrate and use this token. If the access token
is instead bound to the client instance's presented key,
intermediaries no longer have sufficient information to use the
token. They can still, however, gain information about the end user
as well as the actions of the client software.
12.17. Key Distribution
The keys for client instances could be distributed as part of the
deployment process of instances of the client software. For example,
an application installation framework could generate a keypair for
each copy of client software, then both install it into the client
software upon installation and registering that instance with the AS.
Additionally, it's possible for the AS to generate keys to be used
with access tokens that are separate from the keys used by the client
instance to request tokens. In this method, the AS would generate
the asymmetric keypair or symmetric key and return the entire key,
including all private signing information, to the client instance
alongside the access token itself. This approach would make
interception of the return from the token endpoint equivalent to that
of a bearer token, since all information required to use the access
token would be present in the request.
12.18. Interaction Finish Modes and Polling
During the interaction process, the client instance usually hands
control of the user experience over to another component, beit the
system browser, another application, or some action the resource
owner is instructed to take on another device. By using an
interaction finish method, the client instance can be securely
notified by the AS when the interaction is completed and the next
phase of the protocol should occur. This process includes
information that the client instance can use to validate the finish
call from the AS and prevent some injection, session hijacking, and
phishing attacks.
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Some types of client deployment are unable to receive an interaction
finish message. Without an interaction finish method to notify it,
the client instance will need to poll the grant continuation API
while waiting for the resource owner to approve or deny the request.
An attacker could take advantage of this situation by capturing the
interaction start parameters and phishing a legitimate user into
authorizing the attacker's waiting client instance, which would in
turn have no way of associating the completed interaction with the
start of the request.
However, it is important to note that this pattern is practically
indistinguishable from some legitimate use cases. For example, a
smart device emits a code for the resource owner to enter on a
separate device. The smart device has to poll because the expected
behavior is that the interaction will take place on the separate
device, without a way to return information to the original device's
context.
As such, developers need to weigh the risks of forgoing an
interaction finish method against the deployment capabilities of the
client software and its environment. Due to the increased security,
an interaction finish method should be employed whenever possible.
12.19. Storage of Information During Interaction and Continuation
When starting an interactive grant request, a client application has
a number of protocol elements that it needs to manage, including
nonces, references, keys, access tokens, and other elements. During
the interaction process, the client instance usually hands control of
the user experience over to another component, beit the system
browser, another application, or some action the resource owner is
instructed to take on another device. In order for the client
instance to make its continuation call, it will need to recall all of
these protocol elements. Usually this means the client instance will
need to store these protocol elements in some retrievable fashion.
If the security protocol elements are stored on the end-user's
device, such as in browser storage or in local application data
stores, capture and exfiltration of this information could allow an
attacker to continue a pending transaction instead of the client
instance. Client software can make use of secure storage mechanisms,
including hardware-based key and data storage, to prevent such
exfiltration.
Note that in GNAP, the client instance has to choose its interaction
finish URL prior to making the first call to the AS. As such, the
interaction finish URL will often have a unique identifier for the
ongoing request, allowing the client instance to access the correct
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portion of its storage. Since this URL is passed to other parties
and often used through a browser, this URL should not contain any
security-sensitive information that would be valuable to an attacker,
such as any token identifier, nonce, or user information. Instead, a
cryptographically random value is suggested.
12.20. Denial of Service (DoS) through Grant Continuation
When a client instance starts off an interactive process, it will
eventually need to continue the grant request in a subsequent message
to the AS. It's possible for a naive client implementation to
continuously send continuation requests to the AS while waiting for
approval, especially if no interaction finish method is used. Such
constant requests could overwhelm the AS's ability to respond to both
these and other requests.
To mitigate this for well-behaved client software, the continuation
response contains a "wait" parameter that is intended to tell the
client instance how long it should wait until making its next
request. This value can be used to back off client software that is
checking too quickly by returning increasing wait times for a single
client instance.
If client software ignores the "wait" value and makes its
continuation calls too quickly, or if the client software assumes the
absence of the "wait" values means it should poll immediately, the AS
can choose to return errors to the offending client instance,
including possibly canceling the ongoing grant request. With well-
meaning client software these errors can indicate a need to change
the client software's programmed behavior.
12.21. Exhaustion of Random Value Space
Several parts of the GNAP process make use of unguessable randomized
values, such as nonces, tokens, and randomized URLs. Since these
values are intended to be unique, a sufficiently powerful attacker
could make a large number of requests to trigger generation of
randomized values in an attempt to exhaust the random number
generation space. While this attack is particularly applicable to
the AS, client software could likewise be targeted by an attacker
triggering new grant requests against an AS.
To mitigate this, software can ensure that its random values are
chosen from a significantly large pool that exhaustion of that pool
is prohibitive for an attacker. Additionally, the random values can
be time-boxed in such a way as their validity windows are reasonably
short. Since many of the random values used within GNAP are used
within limited portions of the protocol, it is reasonable for a
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particular random value to be valid for only a small amount of time.
For example, the nonces used for interaction finish hash calculation
need only to be valid while the client instance is waiting for the
finish callback and can be functionally expired when the interaction
has completed. Similarly, artifacts like access tokens and the
interaction reference can be limited to have lifetimes tied to their
functional utility. Finally, each different category of artifact
(nonce, token, reference, identifier, etc.) can be generated from a
separate random pool of values instead of a single global value
space.
13. Privacy Considerations
The privacy considerations in this section are modeled after the list
of privacy threats in [[RFC6973]], "Privacy Considerations for
Internet Protocols", and either explain how these threats are
mitigated or advise how the threats relate to GNAP.
13.1. Surveillance
Surveillance is the observation or monitoring of an individual's
communications or activities. Surveillance can be conducted by
observers or eavesdroppers at any point along the communications
path.
GNAP assumes the TLS protection used throughout the spec is intact.
Without the protection of TLS, there are many points throughout the
use of GNAP that would lead to possible surveillance.
13.1.1. Surveillance by the Client
The purpose of GNAP is to authorize clients to be able to access
information on behalf of a user. So while it is expected that the
client may be aware of the user's identity as well as data being
fetched for that user, in some cases the extent of the client may be
beyond what the user is aware of. For example, a client may be
implemented as multiple distinct pieces of software, such as a
logging service or a mobile app that reports usage data to an
external backend service.
13.1.2. Surveillance by the Authorization Server
The role of the authorization server is to manage the authorization
of client instances to protect access to the user's data. In this
role, the authorization server is by definition aware of each
authorization of a client instance by a user. When the authorization
server shares user information with the client instance, it needs to
make sure that it has the permission from that user to do so.
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Additionally, as part of the authorization grant process, the
authorization server may be aware of which resource servers the
client intends to use an access token at. However, it is possible to
design a system using GNAP in which this knowledge is not made
available to the authorization server, such as by avoiding the use of
the "locations" object in the authorization request.
If the authorization server's implementation of access tokens is such
that it requires a resource server call back to the authorization
server to validate them, then the authorization server will be aware
of which resource servers are actively in use and by which users and
which clients. To avoid this possibility, the authorization server
would need to structure access tokens in such a way that they can be
validated by the resource server without notifying the authorization
server that the token is being validated.
13.2. Stored Data
Several parties in the GNAP process are expected to persist data at
least temporarily, if not semi-permanently, for the normal
functioning of the system. If compromised, this could lead to
exposure of sensitive information. This section documents the
potentially sensitive information each party in GNAP is expected to
store for normal operation. Naturally it is possible that any party
is storing information for longer than technically necessary of the
protocol mechanics (such as audit logs, etc).
The authorization server is expected to store subject identifiers for
user indefinitely, in order to be able to include them in the
responses to clients. The authorization server is also expected to
store client key identifiers associated with display information
about the client such as its name and logo.
The client is expected to store its client instance key indefinitely,
in order to authenticate to the authorization server for the normal
functioning of the GNAP flows. Additionally, the client will be
temporarily storing artifacts issued by the authorization server
during a flow, and these artifacts SHOULD be discarded by the client
when the transaction is complete.
The resource server is not required to store any state for its normal
operation. Depending on the implementation of access tokens, the
resource server may need to cache public keys from the authorization
server in order to validate access tokens.
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13.3. Intrusion
Intrusion refers to the ability of various parties to send
unsolicited messages or cause denial of service for unrelated
parties.
If the resource owner is different from the end user, there is an
opportunity for the end user to cause unsolicited messages to be sent
to the resource owner if the system prompts the resource owner for
consent when an end user attempts to access their data.
The format and contents of subject identifiers are intentionally not
defined by GNAP. If the authorization server uses values for subject
identifiers that are also identifiers for communication channels,
(e.g. an email address or phone number), this opens up the
possibility for a client to learn this information when it was not
otherwise authorized to access this kind of data about the user.
13.4. Correlation
The threat of correlation is the combination of various pieces of
information related to an individual in a way that defies their
expectations of what others know about them.
13.4.1. Correlation by Clients
The biggest risk of correlation in GNAP is when an authorization
server returns stable consistent user identifiers to multiple
different applications. In this case, applications created by
different parties would be able to correlate these user identifiers
out of band in order to know which users they have in common.
The most common example of this in practice is tracking for
advertising purposes, such that client A shares their list of user
IDs with an ad platform that is then able to retarget ads to
applications created by other parties. In contrast, a positive
example of correlation is a corporate acquisition where two
previously unrelated clients now do need to be able to identify the
same user between the two clients.
13.4.2. Correlation by Resource Servers
Unrelated resource servers also have an opportunity to correlate
users if the authorization server includes stable user identifiers in
access tokens or in access token introspection responses.
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In some cases a resource server may not actually need to be able to
identify users, (such as a resource server providing access to a
company cafeteria menu which only needs to validate whether the user
is a current employee), so authorization servers should be thoughtful
of when user identifiers are actually necessary to communicate to
resource servers for the functionining of the system.
13.4.3. Correlation by Authorization Servers
Clients are expected to be identified by their client instance key.
If a particular client instance key is used at more than one
authorization server, this could open up the possibility for multiple
unrelated authorization servers to correlate client instances. This
is especially a problem in the common case where a client instance is
used by a single individual, as it would allow the authorization
servers to correlate that individual between them. If this is a
concern of a client, the client should use distinct keys with each
authorization server.
13.5. Disclosure in Shared References
Throughout many parts of GNAP, the parties pass shared references
between each other, sometimes in place of the values themselves. For
example the "interact_ref" value used throughout the flow. These
references are intended to be random strings and should not contain
any private or sensitive data that would potentially leak information
between parties.
14. References
14.1. Normative References
[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", May 2015,
<https://www.rfc-editor.org/info/bcp195>.
[I-D.draft-ietf-gnap-resource-servers]
Richer, J., Parecki, A., and F. Imbault, "Grant
Negotiation and Authorization Protocol Resource Server
Connections", Work in Progress, Internet-Draft, draft-
ietf-gnap-resource-servers-00, 28 April 2021,
<https://www.ietf.org/archive/id/draft-ietf-gnap-resource-
servers-00.txt>.
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[I-D.ietf-httpbis-message-signatures]
Backman, A., Richer, J., and M. Sporny, "HTTP Message
Signatures", Work in Progress, Internet-Draft, draft-ietf-
httpbis-message-signatures-06, 13 August 2021,
<https://www.ietf.org/archive/id/draft-ietf-httpbis-
message-signatures-06.txt>.
[I-D.ietf-oauth-rar]
Lodderstedt, T., Richer, J., and B. Campbell, "OAuth 2.0
Rich Authorization Requests", Work in Progress, Internet-
Draft, draft-ietf-oauth-rar-07, 12 September 2021,
<https://www.ietf.org/archive/id/draft-ietf-oauth-rar-
07.txt>.
[I-D.ietf-oauth-signed-http-request]
Richer, J., Bradley, J., and H. Tschofenig, "A Method for
Signing HTTP Requests for OAuth", Work in Progress,
Internet-Draft, draft-ietf-oauth-signed-http-request-03, 8
August 2016, <https://www.ietf.org/archive/id/draft-ietf-
oauth-signed-http-request-03.txt>.
[I-D.ietf-secevent-subject-identifiers]
Backman, A. and M. Scurtescu, "Subject Identifiers for
Security Event Tokens", Work in Progress, Internet-Draft,
draft-ietf-secevent-subject-identifiers-08, 24 May 2021,
<https://www.ietf.org/archive/id/draft-ietf-secevent-
subject-identifiers-08.txt>.
[OIDC] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0 incorporating
errata set 1", November 2014,
<https://openiD.net/specs/openiD-connect-core-1_0.html>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3230] Mogul, J. and A. Van Hoff, "Instance Digests in HTTP",
RFC 3230, DOI 10.17487/RFC3230, January 2002,
<https://www.rfc-editor.org/info/rfc3230>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
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[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<https://www.rfc-editor.org/info/rfc6750>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<https://www.rfc-editor.org/info/rfc7234>.
[RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX,
PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468,
April 2015, <https://www.rfc-editor.org/info/rfc7468>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8705] Campbell, B., Bradley, J., Sakimura, N., and T.
Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
and Certificate-Bound Access Tokens", RFC 8705,
DOI 10.17487/RFC8705, February 2020,
<https://www.rfc-editor.org/info/rfc8705>.
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[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/info/rfc8792>.
14.2. Informative References
[attack-surfaces]
Axeland, Å. and O. Oueidat, "Security Analysis of Attack
Surfaces on the Grant Negotiation and Authorization
Protocol", 2021,
<https://odr.chalmers.se/handle/20.500.12380/304105>.
[promise-theory]
Burgess, M. and J. Bergstra, "Promise theory", January
2014, <http://markburgess.org/promises.html>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
Appendix A. Document History
* -07
- Replace user handle by opaque identifier
- Added trust relationships
- Added privacy considerations section
- Added security considerations.
* -06
- Removed "capabilities" and "existing_grant" protocol fields.
- Removed separate "instance_id" field.
- Split "interaction_methods_supported" into
"interaction_start_modes_supported" and
"interaction_finish_methods_supported".
- Added AS endpoint to hash calculation to fix mix-up attack.
- Added "privileges" field to resource access request object.
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- Moved client-facing RS response back from GNAP-RS document.
- Removed oauthpop key binding.
- Removed dpop key binding.
- Added example DID identifier.
- Changed token response booleans to flag structure to match
request.
- Updated signature examples to use HTTP Message Signatures.
* -05
- Changed "interaction_methods" to
"interaction_methods_supported".
- Changed "key_proofs" to "key_proofs_supported".
- Changed "assertions" to "assertions_supported".
- Updated discovery and field names for subject formats.
- Add an appendix to provide protocol rationale, compared to
OAuth2.
- Updated subject information definition.
- Refactored the RS-centric components into a new document.
- Updated cryptographic proof of possession methods to match
current reference syntax.
- Updated proofing language to use "signer" and "verifier"
generically.
- Updated cryptographic proof of possession examples.
- Editorial cleanup and fixes.
- Diagram cleanup and fixes.
* -04
- Updated terminology.
- Refactored key presentation and binding.
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- Refactored "interact" request to group start and end modes.
- Changed access token request and response syntax.
- Changed DPoP digest field to 'htd' to match proposed FAPI
profile.
- Include the access token hash in the DPoP message.
- Removed closed issue links.
- Removed function to read state of grant request by client.
- Closed issues related to reading and updating access tokens.
* -03
- Changed "resource client" terminology to separate "client
instance" and "client software".
- Removed OpenID Connect "claims" parameter.
- Dropped "short URI" redirect.
- Access token is mandatory for continuation.
- Removed closed issue links.
- Editorial fixes.
* -02
- Moved all "editor's note" items to GitHub Issues.
- Added JSON types to fields.
- Changed "GNAP Protocol" to "GNAP".
- Editorial fixes.
* -01
- "updated_at" subject info timestamp now in ISO 8601 string
format.
- Editorial fixes.
- Added Aaron and Fabien as document authors.
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* -00
- Initial working group draft.
Appendix B. Compared to OAuth 2.0
GNAP's protocol design differs from OAuth 2.0's in several
fundamental ways:
1. *Consent and authorization flexibility:*
OAuth 2.0 generally assumes the user has access to the a web
browser. The type of interaction available is fixed by the grant
type, and the most common interactive grant types start in the
browser. OAuth 2.0 assumes that the user using the client
software is the same user that will interact with the AS to
approve access.
GNAP allows various patterns to manage authorizations and
consents required to fulfill this requested delegation, including
information sent by the client instance, information supplied by
external parties, and information gathered through the
interaction process. GNAP allows a client instance to list
different ways that it can start and finish an interaction, and
these can be mixed together as needed for different use cases.
GNAP interactions can use a browser, but don't have to. Methods
can use inter-application messaging protocols, out-of-band data
transfer, or anything else. GNAP allows extensions to define new
ways to start and finish an interaction, as new methods and
platforms are expected to become available over time. GNAP is
designed to allow the end-user and the resource owner to be two
different people, but still works in the optimized case of them
being the same party.
2. *Intent registration and inline negotiation:*
OAuth 2.0 uses different "grant types" that start at different
endpoints for different purposes. Many of these require
discovery of several interrelated parameters.
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GNAP requests all start with the same type of request to the same
endpoint at the AS. Next steps are negotiated between the client
instance and AS based on software capabilities, policies
surrounding requested access, and the overall context of the
ongoing request. GNAP defines a continuation API that allows the
client instance and AS to request and send additional information
from each other over multiple steps. This continuation API uses
the same access token protection that other GNAP-protected APIs
use. GNAP allows discovery to optimize the requests but it isn't
required thanks to the negotiation capabilities.
3. *Client instances:*
OAuth 2.0 requires all clients to be registered at the AS and to
use a client_id known to the AS as part of the protocol. This
client_id is generally assumed to be assigned by a trusted
authority during a registration process, and OAuth places a lot
of trust on the client_id as a result. Dynamic registration
allows different classes of clients to get a client_id at
runtime, even if they only ever use it for one request.
GNAP allows the client instance to present an unknown key to the
AS and use that key to protect the ongoing request. GNAP's
client instance identifier mechanism allows for pre-registered
clients and dynamically registered clients to exist as an
optimized case without requiring the identifier as part of the
protocol at all times.
4. *Expanded delegation:*
OAuth 2.0 defines the "scope" parameter for controlling access to
APIs. This parameter has been coopted to mean a number of
different things in different protocols, including flags for
turning special behavior on and off, including the return of data
apart from the access token. The "resource" parameter and RAR
extensions (as defined in [I-D.ietf-oauth-rar]) expand on the
"scope" concept in similar but different ways.
GNAP defines a rich structure for requesting access, with string
references as an optimization. GNAP defines methods for
requesting directly-returned user information, separate from API
access. This information includes identifiers for the current
user and structured assertions. The core GNAP protocol makes no
assumptions or demands on the format or contents of the access
token, but the RS extension allows a negotiation of token formats
between the AS and RS.
5. *Cryptography-based security:*
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OAuth 2.0 uses shared bearer secrets, including the client_secret
and access token, and advanced authentication and sender
constraint have been built on after the fact in inconsistent
ways.
In GNAP, all communication between the client instance and AS is
bound to a key held by the client instance. GNAP uses the same
cryptographic mechanisms for both authenticating the client (to
the AS) and binding the access token (to the RS and the AS).
GNAP allows extensions to define new cryptographic protection
mechanisms, as new methods are expected to become available over
time. GNAP does not have a notion of "public clients" because
key information can always be sent and used dynamically.
6. *Privacy and usable security:*
OAuth 2.0's deployment model assumes a strong binding between the
AS and the RS.
GNAP is designed to be interoperable with decentralized identity
standards and to provide a human-centric authorization layer. In
addition to the core protocol, GNAP that supports various
patterns of communication between RSs and ASs through extensions.
GNAP tries to limit the odds of a consolidation to just a handful
of super-popular AS services.
Appendix C. Component Data Models
While different implementations of this protocol will have different
realizations of all the components and artifacts enumerated here, the
nature of the protocol implies some common structures and elements
for certain components. This appendix seeks to enumerate those
common elements.
TBD: Client has keys, allowed requested resources, identifier(s),
allowed requested subjects, allowed
TBD: AS has "grant endpoint", interaction endpoints, store of trusted
client keys, policies
TBD: Token has RO, user, client, resource list, RS list,
Appendix D. Example Protocol Flows
The protocol defined in this specification provides a number of
features that can be combined to solve many different kinds of
authentication scenarios. This section seeks to show examples of how
the protocol would be applied for different situations.
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Some longer fields, particularly cryptographic information, have been
truncated for display purposes in these examples.
D.1. Redirect-Based User Interaction
In this scenario, the user is the RO and has access to a web browser,
and the client instance can take front-channel callbacks on the same
device as the user. This combination is analogous to the OAuth 2.0
Authorization Code grant type.
The client instance initiates the request to the AS. Here the client
instance identifies itself using its public key.
POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": {
"access": [
{
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
}
],
},
"client": {
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
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"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8..."
}
}
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
}
The AS processes the request and determines that the RO needs to
interact. The AS returns the following response giving the client
instance the information it needs to connect. The AS has also
indicated to the client instance that it can use the given instance
identifier to identify itself in future requests (Section 2.3.1).
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"interact": {
"redirect":
"https://server.example.com/interact/4CF492MLVMSW9MKM",
"push": "MBDOFXG4Y5CVJCX821LH"
}
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue"
},
"instance_id": "7C7C4AZ9KHRS6X63AJAO"
}
The client instance saves the response and redirects the user to the
interaction_url by sending the following HTTP message to the user's
browser.
HTTP 302 Found
Location: https://server.example.com/interact/4CF492MLVMSW9MKM
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The user's browser fetches the AS's interaction URL. The user logs
in, is identified as the RO for the resource being requested, and
approves the request. Since the AS has a callback parameter, the AS
generates the interaction reference, calculates the hash, and
redirects the user back to the client instance with these additional
values added as query parameters.
NOTE: '\' line wrapping per RFC 8792
HTTP 302 Found
Location: https://client.example.net/return/123455\
?hash=p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2\
HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A\
&interact_ref=4IFWWIKYBC2PQ6U56NL1
The client instance receives this request from the user's browser.
The client instance ensures that this is the same user that was sent
out by validating session information and retrieves the stored
pending request. The client instance uses the values in this to
validate the hash parameter. The client instance then calls the
continuation URL and presents the handle and interaction reference in
the request body. The client instance signs the request as above.
POST /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
The AS retrieves the pending request based on the handle and issues a
bearer access token and returns this to the client instance.
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NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [{
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
}]
},
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue"
}
}
D.2. Secondary Device Interaction
In this scenario, the user does not have access to a web browser on
the device and must use a secondary device to interact with the AS.
The client instance can display a user code or a printable QR code.
The client instance is not able to accept callbacks from the AS and
needs to poll for updates while waiting for the user to authorize the
request.
The client instance initiates the request to the AS.
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POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": {
"access": [
"dolphin-metadata", "some other thing"
],
},
"client": "7C7C4AZ9KHRS6X63AJAO",
"interact": {
"start": ["redirect", "user_code"]
}
}
The AS processes this and determines that the RO needs to interact.
The AS supports both redirect URIs and user codes for interaction, so
it includes both. Since there is no "callback" the AS does not
include a nonce, but does include a "wait" parameter on the
continuation section because it expects the client instance to poll
for results.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"interact": {
"redirect": "https://srv.ex/MXKHQ",
"user_code": {
"code": "A1BC-3DFF",
"url": "https://srv.ex/device"
}
},
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue/VGJKPTKC50",
"wait": 60
}
}
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The client instance saves the response and displays the user code
visually on its screen along with the static device URL. The client
instance also displays the short interaction URL as a QR code to be
scanned.
If the user scans the code, they are taken to the interaction
endpoint and the AS looks up the current pending request based on the
incoming URL. If the user instead goes to the static page and enters
the code manually, the AS looks up the current pending request based
on the value of the user code. In both cases, the user logs in, is
identified as the RO for the resource being requested, and approves
the request. Once the request has been approved, the AS displays to
the user a message to return to their device.
Meanwhile, the client instance periodically polls the AS every 60
seconds at the continuation URL. The client instance signs the
request using the same key and method that it did in the first
request.
POST /continue/VGJKPTKC50 HTTP/1.1
Host: server.example.com
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
The AS retrieves the pending request based on the handle and
determines that it has not yet been authorized. The AS indicates to
the client instance that no access token has yet been issued but it
can continue to call after another 60 second timeout.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"continue": {
"access_token": {
"value": "G7YQT4KQQ5TZY9SLSS5E"
},
"uri": "https://server.example.com/continue/ATWHO4Q1WV",
"wait": 60
}
}
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Note that the continuation URL and access token have been rotated
since they were used by the client instance to make this call. The
client instance polls the continuation URL after a 60 second timeout
using this new information.
POST /continue/ATWHO4Q1WV HTTP/1.1
Host: server.example.com
Authorization: GNAP G7YQT4KQQ5TZY9SLSS5E
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
The AS retrieves the pending request based on the URL and access
token, determines that it has been approved, and issues an access
token for the client to use at the RS.
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [
"dolphin-metadata", "some other thing"
]
}
}
D.3. No User Involvement
In this scenario, the client instance is requesting access on its own
behalf, with no user to interact with.
The client instance creates a request to the AS, identifying itself
with its public key and using MTLS to make the request.
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POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
{
"access_token": {
"access": [
"backend service", "nightly-routine-3"
],
},
"client": {
"key": {
"proof": "mtls",
"cert#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2"
}
}
}
The AS processes this and determines that the client instance can ask
for the requested resources and issues an access token.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token",
"access": [
"backend service", "nightly-routine-3"
]
}
}
D.4. Asynchronous Authorization
In this scenario, the client instance is requesting on behalf of a
specific RO, but has no way to interact with the user. The AS can
asynchronously reach out to the RO for approval in this scenario.
The client instance starts the request at the AS by requesting a set
of resources. The client instance also identifies a particular user.
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POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": {
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read", "dolphin-metadata",
{
"type": "financial-transaction",
"actions": [
"withdraw"
],
"identifier": "account-14-32-32-3",
"currency": "USD"
},
"some other thing"
],
},
"client": "7C7C4AZ9KHRS6X63AJAO",
"user": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ]
}
}
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The AS processes this and determines that the RO needs to interact.
The AS determines that it can reach the identified user
asynchronously and that the identified user does have the ability to
approve this request. The AS indicates to the client instance that
it can poll for continuation.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 60
}
}
The AS reaches out to the RO and prompts them for consent. In this
example, the AS has an application that it can push notifications in
to for the specified account.
Meanwhile, the client instance periodically polls the AS every 60
seconds at the continuation URL.
POST /continue HTTP/1.1
Host: server.example.com
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
The AS retrieves the pending request based on the handle and
determines that it has not yet been authorized. The AS indicates to
the client instance that no access token has yet been issued but it
can continue to call after another 60 second timeout.
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HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"continue": {
"access_token": {
"value": "BI9QNW6V9W3XFJK4R02D"
},
"uri": "https://server.example.com/continue",
"wait": 60
}
}
Note that the continuation handle has been rotated since it was used
by the client instance to make this call. The client instance polls
the continuation URL after a 60 second timeout using the new handle.
POST /continue HTTP/1.1
Host: server.example.com
Authorization: GNAP BI9QNW6V9W3XFJK4R02D
Signature-Input: sig1=...
Signature: sig1=...
The AS retrieves the pending request based on the handle and
determines that it has been approved and it issues an access token.
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [
"dolphin-metadata", "some other thing"
]
}
}
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D.5. Applying OAuth 2.0 Scopes and Client IDs
While GNAP is not designed to be directly compatible with OAuth 2.0
[RFC6749], considerations have been made to enable the use of OAuth
2.0 concepts and constructs more smoothly within GNAP.
In this scenario, the client developer has a "client_id" and set of
"scope" values from their OAuth 2.0 system and wants to apply them to
the new protocol. Traditionally, the OAuth 2.0 client developer
would put their "client_id" and "scope" values as parameters into a
redirect request to the authorization endpoint.
NOTE: '\' line wrapping per RFC 8792
HTTP 302 Found
Location: https://server.example.com/authorize\
?client_id=7C7C4AZ9KHRS6X63AJAO\
&scope=read%20write%20dolphin\
&redirect_uri=https://client.example.net/return\
&response_type=code\
&state=123455
Now the developer wants to make an analogous request to the AS using
GNAP. To do so, the client instance makes an HTTP POST and places
the OAuth 2.0 values in the appropriate places.
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POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": {
"access": [
"read", "write", "dolphin"
],
"flags": [ "bearer" ]
},
"client": "7C7C4AZ9KHRS6X63AJAO",
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return?state=123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
}
The "client_id" can be used to identify the client instance's keys
that it uses for authentication, the scopes represent resources that
the client instance is requesting, and the "redirect_uri" and "state"
value are pre-combined into a "finish" URI that can be unique per
request. The client instance additionally creates a nonce to protect
the callback, separate from the state parameter that it has added to
its return URL.
From here, the protocol continues as above.
Appendix E. JSON Structures and Polymorphism
GNAP makes use of polymorphism within the JSON [RFC8259] structures
used for the protocol. Each portion of this protocol is defined in
terms of the JSON data type that its values can take, whether it's a
string, object, array, boolean, or number. For some fields,
different data types offer different descriptive capabilities and are
used in different situations for the same field. Each data type
provides a different syntax to express the same underlying semantic
protocol element, which allows for optimization and simplification in
many common cases.
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Even though JSON is often used to describe strongly typed structures,
JSON on its own is naturally polymorphic. In JSON, the named members
of an object have no type associated with them, and any data type can
be used as the value for any member. In practice, each member has a
semantic type that needs to make sense to the parties creating and
consuming the object. Within this protocol, each object member is
defined in terms of its semantic content, and this semantic content
might have expressions in different concrete data types for different
specific purposes. Since each object member has exactly one value in
JSON, each data type for an object member field is naturally mutually
exclusive with other data types within a single JSON object.
For example, a resource request for a single access token is composed
of an array of resource request descriptions while a request for
multiple access tokens is composed of an object whose member values
are all arrays. Both of these represent requests for access, but the
difference in syntax allows the client instance and AS to
differentiate between the two request types in the same request.
Another form of polymorphism in JSON comes from the fact that the
values within JSON arrays need not all be of the same JSON data type.
However, within this protocol, each element within the array needs to
be of the same kind of semantic element for the collection to make
sense, even when the data types are different from each other.
For example, each aspect of a resource request can be described using
an object with multiple dimensional components, or the aspect can be
requested using a string. In both cases, the resource request is
being described in a way that the AS needs to interpret, but with
different levels of specificity and complexity for the client
instance to deal with. An API designer can provide a set of common
access scopes as simple strings but still allow client software
developers to specify custom access when needed for more complex
APIs.
Extensions to this specification can use different data types for
defined fields, but each extension needs to not only declare what the
data type means, but also provide justification for the data type
representing the same basic kind of thing it extends. For example,
an extension declaring an "array" representation for a field would
need to explain how the array represents something akin to the non-
array element that it is replacing.
Authors' Addresses
Justin Richer (editor)
Bespoke Engineering
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Email: ietf@justin.richer.org
URI: https://bspk.io/
Aaron Parecki
Okta
Email: aaron@parecki.com
URI: https://aaronparecki.com
Fabien Imbault
acert.io
Email: fabien.imbault@acert.io
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