GNAP J. Richer, Ed.
Internet-Draft Bespoke Engineering
Intended status: Standards Track A. Parecki
Expires: 13 January 2022 Okta
F. Imbault
acert.io
12 July 2021
Grant Negotiation and Authorization Protocol Resource Server Connections
draft-ietf-gnap-resource-servers-01
Abstract
GNAP defines a mechanism for delegating authorization to a piece of
software, and conveying that delegation to the software. This
extension defines methods for resource servers (RS) to communicate
with authorization servers (AS) in an interoperable fashion.
Status of This Memo
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This Internet-Draft will expire on 13 January 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Access Token Formats . . . . . . . . . . . . . . . . . . . . 3
3. Resource-Server-Facing API . . . . . . . . . . . . . . . . . 4
3.1. RS-facing AS Discovery . . . . . . . . . . . . . . . . . 4
3.2. Protecting RS requests to the AS . . . . . . . . . . . . 5
3.3. Token Introspection . . . . . . . . . . . . . . . . . . . 6
3.4. Registering a Resource Set . . . . . . . . . . . . . . . 9
4. Deriving a downstream token . . . . . . . . . . . . . . . . . 11
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
6.1. GNAP Token Format Registry . . . . . . . . . . . . . . . 13
6.1.1. Registry Template . . . . . . . . . . . . . . . . . . 13
6.1.2. Initial Registry Contents . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 14
9. Normative References . . . . . . . . . . . . . . . . . . . . 14
Appendix A. Document History . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
The core GNAP protocol does not define any one specific mechanism for
the resource server (RS) to communicate with the authorization server
(AS), allowing the connection between these components to be solved
orthogonally to the core protocol's concerns. For example, the RS
and AS roles could be fulfilled by the same piece of software with
common storage, obviating the need for any connecting protocol.
However, it is often desirable to have the RS and AS communicate at
runtime for a variety of purposes, including allowing the RS to
validate and understand the rights and privileges associated with a
grant of access represented by an access token issued by the AS, or
negotiating the capabilities of either party. These types of
connections are particularly useful for connecting an AS and RS from
different vendors, allowing interoperable distributed deployments of
GNAP-protected systems.
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This specification defines several means for a RS and AS to
communicate these aspects with each other, including structured
access tokens and RS-facing APIs. This specification also discusses
methods for an RS to derive a downstream token for calling another
chained RS.
The means of the authorization server issuing the access token to the
client instance and the means of the client instance presenting the
access token to the resource server are the subject of the GNAP core
protocol specification [I-D.ietf-gnap-core-protocol].
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.
Terminology specific to GNAP is defined in the terminology section of
the core specification [I-D.ietf-gnap-core-protocol], and provides
definitions for the protocol roles: Authorization Server (AS),
Client, Resource Server (RS), Resource Owner (RO), End-user; as well
as the protocol elements: Attribute, Access Token, Grant, Privilege,
Protected Resource, Right, Subject, Subject Information. The same
definitions are used in this document.
2. Access Token Formats
When the AS issues an access token for use at an RS, the RS needs to
have some means of understanding what the access token is for in
order to determine how to respond to the request. The core GNAP
protocol makes no assumptions or demands on the format or contents of
the access token, and in fact the token format and contents are
opaque to the client instance. However, such token formats can be
the topic of agreements between the AS and RS.
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Self-contained structured token formats allow for the conveyance of
information between the AS and RS without requiring the RS to call
the AS at runtime as described in Section 3.3. Structured tokens can
also be used in combination with introspection, allowing the token
itself to carry one class of information and the introspection
response to carry another.
Some token formats, such as Macaroons and Biscuits, allow for the RS
to derive sub-tokens without having to call the AS as described in
Section 4.
The supported token formats can be communicated dynamically at
runtime between the AS and RS in several places.
* The AS can declare its supported token formats as part of RS-
facing discovery Section 3.1
* The RS can require a specific token format be used to access a
registered resource set Section 3.4
* The AS can return the token's format in an introspection response
Section 3.3
In all places where the token format is listed explicitly, it MUST be
one of the registered values in the GNAP Token Formats Registry
Section 6.1.
3. Resource-Server-Facing API
To facilitate runtime and dynamic connections, the AS can offer an
RS-Facing API consisting of one or more of the following optional
pieces.
* Discovery
* Introspection
* Token chaining
* Resource reference registration
3.1. RS-facing AS Discovery
A GNAP AS offering RS-facing services can publish its features on a
well-known discovery document using the URL ".well-known/gnap-as-rs"
appended to the grant request endpoint URL.
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The discovery response is a JSON document [RFC8259] consisting of a
single JSON object with the following fields:
introspection_endpoint (string): OPTIONAL. The URL of the endpoint
offering introspection. 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. Section 3.3
token_formats_supported (array of strings): A list of token formats
supported by this AS. The values in this list MUST be registered
in the GNAP Token Format Registry. Section 6.1
resource_registration_endpoint (string): The URL of the endpoint
offering resource registration. 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. Section 3.4
grant_request_endpoint (string): REQUIRED. The location of the AS's
grant request endpoint, used by the RS to derive downstream access
tokens. 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 be the same URL used by client instances in support of
GNAP requests. Section 4
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 of the request.
3.2. Protecting RS requests to the AS
Unless otherwise specified, the RS MUST protect its calls to the AS
using any of the signature methods defined by GNAP. This signing
method MUST cover all of the appropriate portions of the HTTP request
message, including any body elements, tokens, or headers required for
functionality.
The RS MAY present its keys by reference or by value in a similar
fashion to a client instance calling the AS in the core protocol of
GNAP, described in [I-D.ietf-gnap-core-protocol]. In the protocols
defined here, this takes the form of the resource server identifying
itself using a "key" field or by passing an instance identifier
directly.
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"resource_server": {
"key": {
"proof": "httpsig",
"jwk": {
"kty": "EC",
"crv": "secp256k1",
"kid": "2021-07-06T20:22:03Z",
"x": "-J9OJIZj4nmopZbQN7T8xv3sbeS5-f_vBNSy_EHnBZc",
"y": "sjrS51pLtu3P4LUTVvyAIxRfDV_be2RYpI5_f-Yjivw"
}
}
}
or by reference:
"resource_server": "7C7C4AZ9KHRS6X63AJAO"
The AS MAY require an RS to pre-register its keys or could allow
calls from arbitrary keys in a trust-on-first-use model.
3.3. Token Introspection
The AS issues access tokens representing a set of delegated access
rights to be used at one or more RSs. The AS can offer an
introspection service to allow an RS to validate that a given access
token:
* has been issued by the AS
* has not expired
* has not been revoked
* is appropriate for the RS identified in the call
When the RS receives an access token, it can call the introspection
endpoint at the AS to get token information. [[ See issue #115
(https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/115) ]]
+--------+ +------+ +------+
| Client |--(1)->| RS | | AS |
|Instance| | |--(2)->| |
| | | | | |
| | | |<-(3)--| |
| | | | +------+
| |<-(4)--| |
+--------+ +------+
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1. The client instance calls the RS with its access token.
2. The RS introspects the access token value at the AS. The RS
signs the request with its own key (not the client instance's key
or the token's key).
3. The AS validates the access token value and the Resource Server's
request and returns the introspection response for the token.
4. The RS fulfills the request from the client instance.
The RS signs the request with its own key and sends the access token
as the body of the request.
access_token (string): REQUIRED. The access token value presented
to the RS by the client instance.
proof (string): RECOMMENDED. The proofing method used by the client
instance to bind the token to the RS request.
resource_server (string or object): REQUIRED. The identification
used to authenticate the resource server making this call, either
by value or by reference as described in Section 3.2.
access (array of strings/objects): OPTIONAL. The minimum access
rights required to fulfill the request. This MUST be in the
format described in the Resource Access Rights section of
[I-D.ietf-gnap-core-protocol].
POST /introspect HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Digest: sha256=...
{
"access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"proof": "httpsig",
"resource_server": "7C7C4AZ9KHRS6X63AJAO"
}
The AS MUST validate the access token value and determine if the
token is active. An active access token is defined as a token that
* was issued by the processing AS,
* has not been revoked,
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* has not expired, and
* is appropriate for presentation at the identified RS.
The AS responds with a data structure describing the token's current
state and any information the RS would need to validate the token's
presentation, such as its intended proofing mechanism and key
material.
active (boolean): REQUIRED. If "true", the access token presented
is active, as defined above. If any of the criteria for an active
token are not true, or if the AS is unable to make a determination
(such as the token is not found), the value is set to "false" and
other fields are omitted.
If the access token is active, additional fields from the single
access token response structure defined in
[I-D.ietf-gnap-core-protocol] are included. In particular, these
include the following:
access (array of strings/objects): REQUIRED. The access rights
associated with this access token. This MUST be in the format
described in the Resource Access Rights section of
[I-D.ietf-gnap-core-protocol]. This array MAY be filtered or
otherwise limited for consumption by the identified RS, including
being an empty array.
key (object/string): REQUIRED if the token is bound. The key bound
to the access token, to allow the RS to validate the signature of
the request from the client instance. If the access token is a
bearer token, this MUST NOT be included.
flags (array of strings): OPTIONAL. The set of flags associated
with the access token.
The response MAY include any additional fields defined in an access
token response and MUST NOT include the access token "value" itself.
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HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"active": true,
"access": [
"dolphin-metadata", "some other thing"
],
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeL...."
}
}
}
3.4. Registering a Resource Set
If the RS needs to, it can post a set of resources as described in
the Resource Access Rights section of [I-D.ietf-gnap-core-protocol]
to the AS's resource registration endpoint along with information
about what the RS will need to validate the request.
access (array of objects/strings): REQUIRED. The list of access
rights associated with the request in the format described in the
"Resource Access Rights" section of [I-D.ietf-gnap-core-protocol].
resource_server (string or object): REQUIRED. The identification
used to authenticate the resource server making this call, either
by value or by reference as described in Section 3.2.
token_format_required (string): OPTIONAL. The token format required
to access the identified resource. If the field is omitted, the
token format is at the discretion of the AS. If the AS does not
support the requested token format, the AS MUST return an error to
the RS.
token_introspection_required (boolean): OPTIONAL. If present and
set to "true", the RS expects to make a token introspection
request as described in Section 3.3. If absent or set to "false",
the RS does not anticipate needing to make an introspection
request for tokens relating to this resource set.
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The RS MUST identify itself with its own key and sign the request.
POST /resource HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Digest: ...
{
"access": [
{
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"dolphin-metadata"
],
"resource_server": "7C7C4AZ9KHRS6X63AJAO"
}
The AS responds with a reference appropriate to represent the
resources list that the RS presented in its request as well as any
additional information the RS might need in future requests.
resource_reference (string): REQUIRED. A single string representing
the list of resources registered in the request. The RS MAY make
this handle available to a client instance as part of a discovery
response as described in [I-D.ietf-gnap-core-protocol] or as
documentation to client software developers.
instance_id (string): OPTIONAL. An instance identifier that the RS
can use to refer to itself in future calls to the AS, in lieu of
sending its key by value.
introspection_endpoint (string): OPTIONAL. The introspection
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endpoint of this AS, used to allow the RS to perform token
introspection. Section 3.3
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"resource_reference": "FWWIKYBQ6U56NL1"
}
4. Deriving a downstream token
Some architectures require an RS to act as a client instance and use
a derived access token for a secondary RS. Since the RS is not the
same entity that made the initial grant request, the RS is not
capable of referencing or modifying the existing grant. As such, the
RS needs to request or generate a new token access token for its use
at the secondary RS. This internal secondary token is issued in the
context of the incoming access token.
While it is possible to use a token format (Section 2) that allows
for the RS to generate its own secondary token, the AS can allow the
RS to request this secondary access token using the same process used
by the original client instance to request the primary access token.
Since the RS is acting as its own client instance from the
perspective of GNAP, this process uses the same grant endpoint,
request structure, and response structure as a client instance's
request.
+--------+ +-------+ +------+ +-------+
| Client |--(1)->| RS1 | | AS | | RS2 |
|Instance| | |--(2)->| | | |
| | | |<-(3)--| | | |
| | | | +------+ | |
| | | | | |
| | | |-----------(4)------->| |
| | | |<----------(5)--------| |
| |<-(6)--| | | |
+--------+ +-------+ +-------+
1. The client instance calls RS1 with an access token.
2. RS1 presents that token to the AS to get a derived token for use
at RS2. RS1 indicates that it has no ability to interact with
the RO. Note that RS1 signs its request with its own key, not
the token's key or the client instance's key.
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3. The AS returns a derived token to RS1 for use at RS2.
4. RS1 calls RS2 with the token from (3).
5. RS2 fulfills the call from RS1.
6. RS1 fulfills the call from the original client instance.
If the RS needs to derive a token from one presented to it, it can
request one from the AS by making a token request as described in
[I-D.ietf-gnap-core-protocol] and presenting the existing access
token's value in the "existing_access_token" field.
Since the RS is acting as a client instance, the RS MUST identify
itself with its own key in the "client" field and sign the request
just as any client instance would, as described in Section 3.2.
POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Detached-JWS: ejy0...
{
"access_token": {
"access": [
{
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"dolphin-metadata"
]
},
"client": "7C7C4AZ9KHRS6X63AJAO",
"existing_access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0"
}
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The AS responds with a token for the downstream RS2 as described in
[I-D.ietf-gnap-core-protocol]. The downstream RS2 could repeat this
process as necessary for calling further RS's.
5. Acknowledgements
(TODO: the ACK section should probably be split between the
documents)
6. IANA Considerations
[[ TBD: There are a lot of items in the document that are expandable
through the use of value registries. ]]
6.1. GNAP Token Format Registry
This specification establishes the GNAP Token Format Registry to
define token formats.
6.1.1. Registry Template
6.1.2. Initial Registry Contents
The table below contains the initial contents of the GNAP Token
Format Registry.
+===============+========+====================+===========+
| Name | Status | Description | Reference |
+===============+========+====================+===========+
| jwt-signed | Active | JSON Web Token, | [RFC7519] |
| | | signed with JWS | |
+---------------+--------+--------------------+-----------+
| jwt-encrypted | Active | JSON Web Token, | [RFC7519] |
| | | encrypted with JWE | |
+---------------+--------+--------------------+-----------+
| macaroon | Active | Macaroon | |
+---------------+--------+--------------------+-----------+
| biscuit | Active | Biscuit | |
+---------------+--------+--------------------+-----------+
| zcap | Active | ZCAP | |
+---------------+--------+--------------------+-----------+
Table 1: Initial contents of the GNAP Token Format
Registry.
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7. Security Considerations
[[ TBD: There are a lot of security considerations to add. ]]
All requests have to be over TLS or equivalent as per [BCP195]. Many
handles act as shared secrets, though they can be combined with a
requirement to provide proof of a key as well.
8. Privacy Considerations
[[ TBD: There are a lot of privacy considerations to add. ]]
When introspection is used, the AS is made aware of a particular
token being used at a particular AS, and the AS would not otherwise
have insight into this.
When the client instance receives information about the protecting AS
from an RS, this can be used to derive information about the
resources being protected without releasing the resources themselves.
9. 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.ietf-gnap-core-protocol]
Richer, J., Parecki, A., and F. Imbault, "Grant
Negotiation and Authorization Protocol", Work in Progress,
Internet-Draft, draft-ietf-gnap-core-protocol-05, 28 April
2021, <https://www.ietf.org/archive/id/draft-ietf-gnap-
core-protocol-05.txt>.
[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>.
[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>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
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[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>.
[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>.
Appendix A. Document History
* -01
- Better described RS authentication.
- Added access token format registry.
- Filled out introspection protocol.
- Filled out resource registration protocol.
- Expanded RS-facing discovery mechanisms.
- Moved client-facing RS response back to GNAP core document.
* -00
- Extracted resource server section.
Authors' Addresses
Justin Richer (editor)
Bespoke Engineering
Email: ietf@justin.richer.org
URI: https://bspk.io/
Aaron Parecki
Okta
Email: aaron@parecki.com
URI: https://aaronparecki.com
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Fabien Imbault
acert.io
Email: fabien.imbault@acert.io
URI: https://acert.io/
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