Web Authorization Protocol T. Lodderstedt
Internet-Draft yes.com
Intended status: Standards Track J. Richer
Expires: March 23, 2020 Bespoke Engineering
B. Campbell
Ping Identity
September 20, 2019
OAuth 2.0 Rich Authorization Requests
draft-lodderstedt-oauth-rar-02
Abstract
This document specifies a new parameter "authorization_details" that
is used to carry fine grained authorization data in the OAuth
authorization request.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 23, 2020.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Terminology . . . . . . . . . . . . . . . 3
2. Request parameter "authorization_details" . . . . . . . . . . 3
2.1. Authorization data elements types . . . . . . . . . . . . 5
2.2. Using "authorization_details" . . . . . . . . . . . . . . 7
2.3. Authorization Request Processing . . . . . . . . . . . . 9
2.4. Token Response . . . . . . . . . . . . . . . . . . . . . 10
2.5. Relationship to "resource" parameter . . . . . . . . . . 11
3. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Implementation Considerations . . . . . . . . . . . . . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Document History . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
The OAuth 2.0 authorization framework [RFC6749] defines the parameter
"scope" that allows OAuth clients to specify the requested scope,
i.e., the permission, of an access token. This mechanism is
sufficient to implement static scenarios and coarse-grained
authorization requests, such as "give me read access to the resource
owner's profile" but it is not sufficient to specify fine-grained
authorization requirements, such as "please let me make a payment
with the amount of 45 Euros" or "please give me read access to folder
A and write access to file X".
This draft introduces a new parameter "authorization_details" that
allows clients to specify their fine-grained authorization
requirements using the expressiveness of JSON data structures.
For example, a request for payment authorization can be represented
using a JSON object like this:
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[
{
"type": "payment_initiation",
"instructedAmount":{
"currency":"EUR",
"amount":"123.50"
},
"debtorAccount":{
"iban":"DE40100100103307118608"
},
"creditorName":"Merchant123",
"creditorAccount":{
"iban":"DE02100100109307118603"
},
"remittanceInformationUnstructured":"Ref Number Merchant"
}
]
In addition to facilitating custom authorization requests, this draft
also introduces a set of common data type fields for use across
different APIs.
For a comprehensive discussion of the challenges arising from new use
cases in the open banking and electronic signing spaces see
[transaction-authorization].
1.1. Conventions and 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 specification uses the terms "access token", "refresh token",
"authorization server", "resource server", "authorization endpoint",
"authorization request", "authorization response", "token endpoint",
"grant type", "access token request", "access token response", and
"client" defined by The OAuth 2.0 Authorization Framework [RFC6749].
2. Request parameter "authorization_details"
The request parameter "authorization_details" contains a JSON array
of JSON objects. Each JSON object contains the data to specify the
authorization requirements for a certain type of resource. The type
of resource or access requirement is determined by the "type" field.
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This example shows the specification of authorization details for a
payment initiation transaction:
[
{
"type": "payment_initiation",
"actions": ["initiate", "status", "cancel"],
"locations":[
"https://example.com/payments"
],
"instructedAmount":{
"currency":"EUR",
"amount":"123.50"
},
"debtorAccount":{
"iban":"DE40100100103307118608"
},
"creditorName":"Merchant123",
"creditorAccount":{
"iban":"DE02100100109307118603"
},
"remittanceInformationUnstructured":"Ref Number Merchant"
}
]
This example shows a combined request asking for access to account
information and permission to initiate a payment:
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[
{
"type": "account_information",
"actions":
["list_accounts", "read_balances", "read_transactions"],
"identifier": "abc-123565",
"locations": [
"https://example.com/accounts"
]
},
{
"type": "payment_initiation",
"actions": ["initiate", "status", "cancel"],
"locations":[
"https://example.com/payments"
],
"instructedAmount":{
"currency":"EUR",
"amount":"123.50"
},
"debtorAccount":{
"iban":"DE40100100103307118608"
},
"creditorName":"Merchant123",
"creditorAccount":{
"iban":"DE02100100109307118603"
},
"remittanceInformationUnstructured":"Ref Number Merchant"
}
]
The JSON objects with "type" fields of "account_information" and
"payment_initiation" represent the different authorization data to be
used by the AS to ask for consent and MUST subsequently also be made
available to the respective resource servers. The array MAY contain
several elements of the same "type".
2.1. Authorization data elements types
This draft defines a set of common data elements that are designed to
be usable across different types of APIs. These data elements MAY be
combined in different ways depending on the needs of the API. Unless
otherwise noted, all data elements are OPTIONAL.
type:
The type of resource request as a string. This field MAY define
which other elements are allowed in the request. This element is
REQUIRED.
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locations:
An array of strings representing the location of the resource or
resource server. This is typically composed of URIs.
actions:
An array of strings representing the kinds of actions to be taken
at the resource. The values of the strings are determined by the
API being protected.
data:
An array of strings representing the kinds of data being requested
from the resource.
identifier:
A string identifier indicating a specific resource available at
the API.
An API MAY define its own extensions, subject to the "type" of the
request. It is assumed that the full structure of each of the
authorization data elements is tailored to the needs of a certain
application, API, or resource type. The example structures shown
above are based on certain kinds of APIs that can be found in the
Open Banking space.
Note: Applications MUST ensure that their authorization data types do
not collide. This is either achieved by using a namespace under the
control of the entity defining the type name or by registering the
type with the new "OAuth Authorization Data Type Registry" (see
Section 8).
The following example shows how an implementation could utilize the
namespace "https://scheme.example.org/" to ensure collision resistant
element names.
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{
"type":"https://scheme.example.org/files",
"locations":[
"https://example.com/files"
],
"permissions":[
{
"path":"/myfiles/A",
"access":[
"read"
]
},
{
"path":"/myfiles/A/X",
"access":[
"read",
"write"
]
}
]
}
2.2. Using "authorization_details"
The request parameter can be used anywhere where the "scope"
parameter is used, examples include:
o Authorization requests as specified in [RFC6749],
o Access token requests as specified in [RFC6749],
o Request objects as specified in [I-D.ietf-oauth-jwsreq],
o Device Authorization Request as specified in [RFC8628].
Parameter encoding is determined by the respective context.
In the context of an authorization request according to [RFC6749],
the parameter is encoded using the "application/x-www-form-
urlencoded" format as shown in the following example (JSON string
trimmed for brevity):
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GET /authorize?response_type=code&client_id=s6BhdRkqt3
&state=af0ifjsldkj
&redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb
&code_challenge_method=S256
&code_challenge=K2-ltc83acc4h0c9w6ESC_rEMTJ3bww-uCHaoeK1t8U
&authorization_details=%5B%7B%22type%22%3A%22https%3A%2F%2F
www.someorg.com%2Fpayment_initiation%22%2C%22actions%22%3A%5
B%22initiate%22%2C%22status%22%2C%22cancel%22%5D%2C%22locat
ions%22%3A%5B%22https%3A%2F%2Fexample.com%2Fpayments%22%5D%
2C%22instructedAmount%22%3A%7B%22currency%22%3A%22EUR%22%2C
%22amount%22%3A%22123.50%22%7D%2C%22debtorAccount%22%3A%7B%
22iban%22%3A%22DE40100100103307118608%22%7D%2C%22creditorNa
me%22%3A%22Merchant123%22%2C%22creditorAccount%22%3A%7B%22i
ban%22%3A%22DE02100100109307118603%22%7D%2C%22remittanceInf
ormationUnstructured%22%3A%22Ref%20Number%20Merchant%22%7D%
5D%0A%20%20%20 HTTP/1.1
Host: server.example.com
In the context of a request object as specified in
[I-D.ietf-oauth-jwsreq], "authorization_details" is added as another
top level JSON element.
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{
"iss":"s6BhdRkqt3",
"aud":"https://server.example.com",
"response_type":"code",
"client_id":"s6BhdRkqt3",
"redirect_uri":"https://client.example.com/cb",
"state":"af0ifjsldkj",
"code_challenge_method":"S256",
"code_challenge":"K2-ltc83acc4h0c9w6ESC_rEMTJ3bww-uCHaoeK1t8U",
"authorization_details":[
{
"type": "https://www.someorg.com/payment_initiation",
"actions": ["initiate", "status", "cancel"],
"locations":[
"https://example.com/payments"
],
"instructedAmount":{
"currency":"EUR",
"amount":"123.50"
},
"debtorAccount":{
"iban":"DE40100100103307118608"
},
"creditorName":"Merchant123",
"creditorAccount":{
"iban":"DE02100100109307118603"
},
"remittanceInformationUnstructured":"Ref Number Merchant"
}
]
}
Note: Authorization request URIs containing authorization details in
a request parameter or a request object can become very long.
Implementers SHOULD therefore consider using the "request_uri"
parameter as defined in [I-D.ietf-oauth-jwsreq], potentially in
combination with the pushed request object mechanism as defined in
[I-D.lodderstedt-oauth-par] to pass authorization details in a
reliable and secure manner.
2.3. Authorization Request Processing
Based on the data provided in the "authorization_details" parameter
the AS will ask the user for consent to the requested access
permissions.
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Note: The AS is supposed to merge the authorization requirements
given in the "scope" parameter and the "authorization_details"
parameter if both are present in the authorization request.
The AS MUST refuse to process any unknown authorization data type.
If the "authorization_details" contains any unknown authorization
data type, the AS MUST abort processing and respond with an error
"invalid_scope" to the client.
If the resource owner grants the client the requested access, the AS
will issue tokens to the client that are associated with the
respective "authorization_details".
The AS MUST make the "authorization_details" available to the
respective resource servers. The AS MAY add the
"authorization_details" element to access tokens in JWT format and to
Token Introspection responses.
The AS MUST take into consideration the privacy implications when
sharing authorization details with the resource servers. The AS
SHOULD share this data with the resource servers on a "need to know"
basis.
2.4. Token Response
In addition to the token response parameters as defined in [RFC6749],
the authorization server MUST also return the authorization details
as granted by the resource owner and assigned to the respective
access token.
This is shown in the following example:
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HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-cache, no-store
{
"access_token":"2YotnFZFEjr1zCsicMWpAA",
"token_type":"example",
"expires_in":3600,
"refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA",
"authorization_details":[
{
"type": "https://www.someorg.com/payment_initiation",
"actions": ["initiate", "status", "cancel"],
"locations":[
"https://example.com/payments"
],
"instructedAmount":{
"currency":"EUR",
"amount":"123.50"
},
"debtorAccount":{
"iban":"DE40100100103307118608"
},
"creditorName":"Merchant123",
"creditorAccount":{
"iban":"DE02100100109307118603"
},
"remittanceInformationUnstructured":"Ref Number Merchant"
}
]
}
2.5. Relationship to "resource" parameter
[I-D.ietf-oauth-resource-indicators] defines the request parameter
"resource" indicating to the AS the resource(s) where the client
intends to use the access tokens issued based on a certain grant.
This mechanism is a way to audience-restrict access tokens and to
allow the AS to create resource specific access tokens.
This draft can be used in conjunction with
[I-D.ietf-oauth-resource-indicators] in the same way as the "scope"
parameter. The AS is supposed to narrow down the authorization
details and respective permissions to the needs of the particular
resource when minting an access token.
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This depends, however, on the AS to know what authorization details
are relevant for what RS. The parameter introduced in this
specification can also be combined with the concept of resource
indicators to make this relationship explicit. This enables the AS
to narrow down the privileges of an access token to specific
permissions for individual operations on specific resources (see
[I-D.ietf-oauth-security-topics], section-3.3).
The "locations" and the "identifier" elements together allow the AS
to determine the resource a client wants to access as shown in
following example:
[
{
"type": "https://scheme.example.org/storage":
"locations":["https://storage.example.com"],
"identifier":"/shared/group1",
"actions":[
"read"
]
}
}
The AS MUST respect those values when deciding whether a certain
element is placed into a (structured) access token or token
introspection response.
3. Metadata
The AS advertises support for "authorization_details" using the
metadata parameter "authorization_details_supported" of type boolean.
The authorization data types supported can be determined using the
metadata parameter "authorization_data_types_supported", which is an
JSON array.
Clients announce the authorization data types they use in the new
dynamic client registration parameter "authorization_data_types".
The registration of new authorization data types with the AS is out
of scope of this draft.
4. Implementation Considerations
The scheme and processing will vary significantly among different
authorization data types. Any implementation of this draft is
therefore supposed to allow the customization of the user consent and
the handling of access token data.
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One option would be to have a mechanism allowing the registration of
extension modules, each of them responsible for rendering the
respective user consent and any transformation needed to provide the
data needed to the resource server by way of structured access tokens
or token introspection responses.
5. Security Considerations
Authorization details are sent through the user agent in case of an
OAuth authorization request, which makes them vulnerable to
modifications by the user. In order to ensure their integrity, the
client SHOULD send authorization details in a signed request object
as defined in [I-D.ietf-oauth-jwsreq] or use the "request_uri"
authorization request parameter as defined in [I-D.ietf-oauth-jwsreq]
to pass the URI of the request object to the authorization server.
6. Privacy Considerations
Implementers MUST design and use authorization details in a privacy
preserving manner.
Any sensitive personal data included in authorization details MUST be
prevented from leaking, e.g., through referrer headers.
Implementation options include encrypted request objects as defined
in [I-D.ietf-oauth-jwsreq] or transmission of authorization details
via end-to-end encrypted connections between client and authorization
server by utilizing the "request_uri" authorization request parameter
as defined in [I-D.ietf-oauth-jwsreq].
Even if the request data are encrypted, an attacker could use the
authorization server to learn the user data by injecting the
encrypted request data into an authorization request on a device
under his control and use the authorization server's user consent
screens to show the (decrypted) user data in the clear.
Implementations MUST consider this attacker vector and implement
appropriate counter measures, e.g. by only showing portions of the
data or, if possible, determing whether the assumed user context is
still the same (after user authentication).
7. Acknowledgements
We would would like to thank Daniel Fett, Sebastian Ebling, Dave
Tonge, Mike Jones, Nat Sakimura, and Rob Otto for their valuable
feedback during the preparation of this draft.
We would also like to thank Daniel Fett, Dave Tonge and Aaron Parecki
for their valuable feedback to this draft.
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8. IANA Considerations
TBD
o "authorization_details" as JWT claim
o "authorization_details_supported" and
"authorization_data_types_supported" as metadata parameters
o "authorization_data_types" as dynamic client registration
parameter
o establish authorization data type registry
9. References
9.1. Normative References
[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>.
[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>.
[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>.
[RFC8628] Denniss, W., Bradley, J., Jones, M., and H. Tschofenig,
"OAuth 2.0 Device Authorization Grant", RFC 8628,
DOI 10.17487/RFC8628, August 2019,
<https://www.rfc-editor.org/info/rfc8628>.
9.2. Informative References
[I-D.ietf-oauth-jwsreq]
Sakimura, N. and J. Bradley, "The OAuth 2.0 Authorization
Framework: JWT Secured Authorization Request (JAR)",
draft-ietf-oauth-jwsreq-19 (work in progress), June 2019.
[I-D.ietf-oauth-resource-indicators]
Campbell, B., Bradley, J., and H. Tschofenig, "Resource
Indicators for OAuth 2.0", draft-ietf-oauth-resource-
indicators-08 (work in progress), September 2019.
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[I-D.ietf-oauth-security-topics]
Lodderstedt, T., Bradley, J., Labunets, A., and D. Fett,
"OAuth 2.0 Security Best Current Practice", draft-ietf-
oauth-security-topics-13 (work in progress), July 2019.
[I-D.lodderstedt-oauth-par]
Lodderstedt, T., Campbell, B., Sakimura, N., Tonge, D.,
and F. Skokan, "OAuth 2.0 Pushed Authorization Requests",
draft-lodderstedt-oauth-par-00 (work in progress),
September 2019.
[transaction-authorization]
Lodderstedt, T., "Transaction Authorization or why we need
to re-think OAuth scopes", Apr 2019, <https://medium.com/
oauth-2/transaction-authorization-or-why-we-need-to-re-
think-oauth-scopes-2326e2038948>.
Appendix A. Document History
[[ To be removed from the final specification ]]
-02
o Added Security Considerations
o Added Privacy Considerations
o Added notes on URI size and authorization details
o Added requirement to return the effective authorization details
granted by the resource owner in the token response
o changed "authorization_details" structure from object to array
o added Justin Richer & Brian Campbell as Co-Authors
-00 / -01
o first draft
Authors' Addresses
Torsten Lodderstedt
yes.com
Email: torsten@lodderstedt.net
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Justin Richer
Bespoke Engineering
Email: ietf@justin.richer.org
Brian Campbell
Ping Identity
Email: bcampbell@pingidentity.com
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