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Internet Engineering Task Force (IETF) T. Lodderstedt
Request for Comments: 9126 yes.com
Category: Standards Track B. Campbell
ISSN: 2070-1721 Ping Identity
N. Sakimura
NAT.Consulting
D. Tonge
Moneyhub Financial Technology
F. Skokan
Auth0
September 2021
OAuth 2.0 Pushed Authorization Requests
Abstract
This document defines the pushed authorization request (PAR)
endpoint, which allows clients to push the payload of an OAuth 2.0
authorization request to the authorization server via a direct
request and provides them with a request URI that is used as
reference to the data in a subsequent call to the authorization
endpoint.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9126.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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 and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction
1.1. Introductory Example
1.2. Conventions and Terminology
2. Pushed Authorization Request Endpoint
2.1. Request
2.2. Successful Response
2.3. Error Response
2.4. Management of Client Redirect URIs
3. The "request" Request Parameter
4. Authorization Request
5. Authorization Server Metadata
6. Client Metadata
7. Security Considerations
7.1. Request URI Guessing
7.2. Open Redirection
7.3. Request Object Replay
7.4. Client Policy Change
7.5. Request URI Swapping
8. Privacy Considerations
9. IANA Considerations
9.1. OAuth Authorization Server Metadata
9.2. OAuth Dynamic Client Registration Metadata
9.3. OAuth URI Registration
10. References
10.1. Normative References
10.2. Informative References
Acknowledgements
Authors' Addresses
1. Introduction
This document defines the pushed authorization request (PAR)
endpoint, which enables an OAuth [RFC6749] client to push the payload
of an authorization request directly to the authorization server. A
request URI value is received in exchange; it is used as reference to
the authorization request payload data in a subsequent call to the
authorization endpoint via the user agent.
In OAuth [RFC6749], authorization request parameters are typically
sent as URI query parameters via redirection in the user agent. This
is simple but also yields challenges:
* There is no cryptographic integrity and authenticity protection.
An attacker could, for example, modify the scope of access
requested or swap the context of a payment transaction by changing
scope values. Although protocol facilities exist to enable
clients or users to detect some such changes, preventing
modifications early in the process is a more robust solution.
* There is no mechanism to ensure confidentiality of the request
parameters. Although HTTPS is required for the authorization
endpoint, the request data passes through the user agent in the
clear, and query string data can inadvertently leak to web server
logs and to other sites via the referrer. The impact of such
leakage can be significant, if personally identifiable information
or other regulated data is sent in the authorization request
(which might well be the case in identity, open banking, and
similar scenarios).
* Authorization request URLs can become quite large, especially in
scenarios requiring fine-grained authorization data, which might
cause errors in request processing.
JWT-Secured Authorization Request (JAR) [RFC9101] provides solutions
for the security challenges by allowing OAuth clients to wrap
authorization request parameters in a Request Object, which is a
signed and optionally encrypted JSON Web Token (JWT) [RFC7519]. In
order to cope with the size restrictions, JAR introduces the
"request_uri" parameter that allows clients to send a reference to a
Request Object instead of the Request Object itself.
This document complements JAR by providing an interoperable way to
push the payload of an authorization request directly to the
authorization server in exchange for a "request_uri" value usable at
the authorization server in a subsequent authorization request.
PAR fosters OAuth security by providing clients a simple means for a
confidential and integrity-protected authorization request. Clients
requiring an even higher security level, especially cryptographically
confirmed non-repudiation, are able to use JWT-based Request Objects
as defined by [RFC9101] in conjunction with PAR.
PAR allows the authorization server to authenticate the client before
any user interaction happens. The increased confidence in the
identity of the client during the authorization process allows the
authorization server to refuse illegitimate requests much earlier in
the process, which can prevent attempts to spoof clients or otherwise
tamper with or misuse an authorization request.
Note that HTTP "POST" requests to the authorization endpoint via the
user agent, as described in Section 3.1 of [RFC6749] and
Section 3.1.2.1 of [OIDC], could also be used to cope with the
request size limitations described above. However, it's only
optional per [RFC6749], and, even when supported, it is a viable
option for conventional web applications but is prohibitively
difficult to use with installed mobile applications. As described in
[RFC8252], those apps use platform-specific APIs to open the
authorization request URI in the system browser. When a mobile app
launches a browser, however, the resultant initial request is
constrained to use the "GET" method. Using "POST" for the
authorization request would require the app to first direct the
browser to open a URI that the app controls via "GET" while somehow
conveying the sizable authorization request payload and then having
the resultant response contain the content and script to initiate a
cross-site form "POST" towards the authorization server. PAR is
simpler to use and has additional security benefits, as described
above.
1.1. Introductory Example
In conventional OAuth 2.0, a client typically initiates an
authorization request by directing the user agent to make an HTTP
request like the following to the authorization server's
authorization endpoint (extra line breaks and indentation for display
purposes only):
GET /authorize?response_type=code
&client_id=CLIENT1234&state=duk681S8n00GsJpe7n9boxdzen
&redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb HTTP/1.1
Host: as.example.com
Such a request could instead be pushed directly to the authorization
server by the client with a "POST" request to the PAR endpoint as
illustrated in the following example (extra line breaks and spaces
for display purposes only). The client can authenticate (e.g., using
JWT client assertion-based authentication as shown) because the
request is made directly to the authorization server.
POST /as/par HTTP/1.1
Host: as.example.com
Content-Type: application/x-www-form-urlencoded
&response_type=code
&client_id=CLIENT1234&state=duk681S8n00GsJpe7n9boxdzen
&redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb
&client_assertion_type=
urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_assertion=eyJraWQiOiI0MiIsImFsZyI6IkVTMjU2In0.eyJpc3MiOiJDTE
lFTlQxMjM0Iiwic3ViIjoiQ0xJRU5UMTIzNCIsImF1ZCI6Imh0dHBzOi8vc2VydmVyL
mV4YW1wbGUuY29tIiwiZXhwIjoxNjI1ODY4ODc4fQ.Igw8QrpAWRNPDGoWGRmJumLBM
wbLjeIYwqWUu-ywgvvufl_0sQJftNs3bzjIrP0BV9rRG-3eI1Ksh0kQ1CwvzA
The authorization server responds with a request URI:
HTTP/1.1 201 Created
Cache-Control: no-cache, no-store
Content-Type: application/json
{
"request_uri": "urn:example:bwc4JK-ESC0w8acc191e-Y1LTC2",
"expires_in": 90
}
The client uses the request URI value to create the subsequent
authorization request by directing the user agent to make an HTTP
request to the authorization server's authorization endpoint like the
following (extra line breaks and indentation for display purposes
only):
GET /authorize?client_id=CLIENT1234
&request_uri=urn%3Aexample%3Abwc4JK-ESC0w8acc191e-Y1LTC2 HTTP/1.1
Host: as.example.com
1.2. 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", "authorization
server", "authorization endpoint", "authorization request", "token
endpoint", and "client" defined by "The OAuth 2.0 Authorization
Framework" [RFC6749].
2. Pushed Authorization Request Endpoint
The pushed authorization request endpoint is an HTTP API at the
authorization server that accepts HTTP "POST" requests with
parameters in the HTTP request message body using the "application/x-
www-form-urlencoded" format. This format has a character encoding of
UTF-8, as described in Appendix B of [RFC6749]. The PAR endpoint URL
MUST use the "https" scheme.
Authorization servers supporting PAR SHOULD include the URL of their
pushed authorization request endpoint in their authorization server
metadata document [RFC8414] using the
"pushed_authorization_request_endpoint" parameter as defined in
Section 5.
The endpoint accepts the authorization request parameters defined in
[RFC6749] for the authorization endpoint as well as all applicable
extensions defined for the authorization endpoint. Some examples of
such extensions include Proof Key for Code Exchange (PKCE) [RFC7636],
Resource Indicators [RFC8707], and OpenID Connect (OIDC) [OIDC]. The
endpoint MAY also support sending the set of authorization request
parameters as a Request Object according to [RFC9101] and Section 3
of this document.
The rules for client authentication as defined in [RFC6749] for token
endpoint requests, including the applicable authentication methods,
apply for the PAR endpoint as well. If applicable, the
"token_endpoint_auth_method" client metadata parameter [RFC7591]
indicates the registered authentication method for the client to use
when making direct requests to the authorization server, including
requests to the PAR endpoint. Similarly, the
"token_endpoint_auth_methods_supported" authorization server metadata
[RFC8414] parameter lists client authentication methods supported by
the authorization server when accepting direct requests from clients,
including requests to the PAR endpoint.
Due to historical reasons, there is potential ambiguity regarding the
appropriate audience value to use when employing JWT client
assertion-based authentication (defined in Section 2.2 of [RFC7523]
with "private_key_jwt" or "client_secret_jwt" authentication method
names per Section 9 of [OIDC]). To address that ambiguity, the
issuer identifier URL of the authorization server according to
[RFC8414] SHOULD be used as the value of the audience. In order to
facilitate interoperability, the authorization server MUST accept its
issuer identifier, token endpoint URL, or pushed authorization
request endpoint URL as values that identify it as an intended
audience.
2.1. Request
A client sends the parameters that comprise an authorization request
directly to the PAR endpoint. A typical parameter set might include:
"client_id", "response_type", "redirect_uri", "scope", "state",
"code_challenge", and "code_challenge_method" as shown in the example
below. However, the pushed authorization request can be composed of
any of the parameters applicable for use at the authorization
endpoint, including those defined in [RFC6749] as well as all
applicable extensions. The "request_uri" authorization request
parameter is one exception, and it MUST NOT be provided.
The request also includes, as appropriate for the given client, any
additional parameters necessary for client authentication (e.g.,
"client_secret" or "client_assertion" and "client_assertion_type").
Such parameters are defined and registered for use at the token
endpoint but are applicable only for client authentication. When
present in a pushed authorization request, they are relied upon only
for client authentication and are not germane to the authorization
request itself. Any token endpoint parameters that are not related
to client authentication have no defined meaning for a pushed
authorization request. The "client_id" parameter is defined with the
same semantics for both authorization requests and requests to the
token endpoint; as a required authorization request parameter, it is
similarly required in a pushed authorization request.
The client constructs the message body of an HTTP "POST" request with
parameters formatted with "x-www-form-urlencoded" using a character
encoding of UTF-8, as described in Appendix B of [RFC6749]. If
applicable, the client also adds its authentication credentials to
the request header or the request body using the same rules as for
token endpoint requests.
This is illustrated by the following example (extra line breaks in
the message body for display purposes only):
POST /as/par HTTP/1.1
Host: as.example.com
Content-Type: application/x-www-form-urlencoded
response_type=code&state=af0ifjsldkj&client_id=s6BhdRkqt3
&redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb
&code_challenge=K2-ltc83acc4h0c9w6ESC_rEMTJ3bww-uCHaoeK1t8U
&code_challenge_method=S256&scope=account-information
&client_assertion_type=
urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_assertion=eyJraWQiOiJrMmJkYyIsImFsZyI6IlJTMjU2In0.eyJpc3Mi
OiJzNkJoZFJrcXQzIiwic3ViIjoiczZCaGRSa3F0MyIsImF1ZCI6Imh0dHBzOi8vc
2VydmVyLmV4YW1wbGUuY29tIiwiZXhwIjoxNjI1ODY5Njc3fQ.te4IdnP_DK4hWrh
TWA6fyhy3fxlAQZAhfA4lmzRdpoP5uZb-E90R5YxzN1YDA8mnVdpgj_Bx1lG5r6se
f5TlckApA3hahhC804dcqlE4naEmLISmN1pds2WxTMOUzZY8aKKSDzNTDqhyTgE-K
dTb3RafRj7tdZb09zWs7c_moOvfVcQIoy5zz1BvLQKW1Y8JsYvdpu2AvpxRPbcP8W
yeW9B6PL6_fy3pXYKG3e-qUcvPa9kan-mo9EoSgt-YTDQjK1nZMdXIqTluK9caVJE
RWW0fD1Y11_tlOcJn-ya7v7d8YmFyJpkhZfm8x1FoeH0djEicXTixEkdRuzsgUCm6
GQ
The authorization server MUST process the request as follows:
1. Authenticate the client in the same way as at the token endpoint
(Section 2.3 of [RFC6749]).
2. Reject the request if the "request_uri" authorization request
parameter is provided.
3. Validate the pushed request as it would an authorization request
sent to the authorization endpoint. For example, the
authorization server checks whether the redirect URI matches one
of the redirect URIs configured for the client and also checks
whether the client is authorized for the scope for which it is
requesting access. This validation allows the authorization
server to refuse unauthorized or fraudulent requests early. The
authorization server MAY omit validation steps that it is unable
to perform when processing the pushed request; however, such
checks MUST then be performed when processing the authorization
request at the authorization endpoint.
The authorization server MAY allow clients with authentication
credentials to establish per-authorization-request redirect URIs with
every pushed authorization request. Described in more detail in
Section 2.4, this is possible since, in contrast to [RFC6749], this
specification gives the authorization server the ability to
authenticate clients and validate client requests before the actual
authorization request is performed.
2.2. Successful Response
If the verification is successful, the server MUST generate a request
URI and provide it in the response with a "201" HTTP status code.
The following parameters are included as top-level members in the
message body of the HTTP response using the "application/json" media
type as defined by [RFC8259].
request_uri
The request URI corresponding to the authorization request posted.
This URI is a single-use reference to the respective request data
in the subsequent authorization request. The way the
authorization process obtains the authorization request data is at
the discretion of the authorization server and is out of scope of
this specification. There is no need to make the authorization
request data available to other parties via this URI.
expires_in
A JSON number that represents the lifetime of the request URI in
seconds as a positive integer. The request URI lifetime is at the
discretion of the authorization server but will typically be
relatively short (e.g., between 5 and 600 seconds).
The format of the "request_uri" value is at the discretion of the
authorization server, but it MUST contain some part generated using a
cryptographically strong pseudorandom algorithm such that it is
computationally infeasible to predict or guess a valid value (see
Section 10.10 of [RFC6749] for specifics). The authorization server
MAY construct the "request_uri" value using the form
"urn:ietf:params:oauth:request_uri:<reference-value>" with
"<reference-value>" as the random part of the URI that references the
respective authorization request data.
The "request_uri" value MUST be bound to the client that posted the
authorization request.
The following is an example of such a response:
HTTP/1.1 201 Created
Content-Type: application/json
Cache-Control: no-cache, no-store
{
"request_uri":
"urn:ietf:params:oauth:request_uri:6esc_11ACC5bwc014ltc14eY22c",
"expires_in": 60
}
2.3. Error Response
The authorization server returns an error response with the same
format as is specified for error responses from the token endpoint in
Section 5.2 of [RFC6749] using the appropriate error code from
therein or from Section 4.1.2.1 of [RFC6749]. In those cases where
Section 4.1.2.1 of [RFC6749] prohibits automatic redirection with an
error back to the requesting client and hence doesn't define an error
code (for example, when the request fails due to a missing, invalid,
or mismatching redirection URI), the "invalid_request" error code can
be used as the default error code. Error codes defined by the OAuth
extension can also be used when such an extension is involved in the
initial processing of the authorization request that was pushed.
Since initial processing of the pushed authorization request does not
involve resource owner interaction, error codes related to user
interaction, such as "consent_required" defined by [OIDC], are never
returned.
If the client is required to use signed Request Objects, by either
the authorization server or the client policy (see [RFC9101],
Section 10.5), the authorization server MUST only accept requests
complying with the definition given in Section 3 and MUST refuse any
other request with HTTP status code 400 and error code
"invalid_request".
In addition to the above, the PAR endpoint can also make use of the
following HTTP status codes:
405: If the request did not use the "POST" method, the authorization
server responds with an HTTP 405 (Method Not Allowed) status
code.
413: If the request size was beyond the upper bound that the
authorization server allows, the authorization server responds
with an HTTP 413 (Payload Too Large) status code.
429: If the number of requests from a client during a particular
time period exceeds the number the authorization server allows,
the authorization server responds with an HTTP 429 (Too Many
Requests) status code.
The following is an example of an error response from the PAR
endpoint:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-cache, no-store
{
"error": "invalid_request",
"error_description":
"The redirect_uri is not valid for the given client"
}
2.4. Management of Client Redirect URIs
OAuth 2.0 [RFC6749] allows clients to use unregistered "redirect_uri"
values in certain circumstances or for the authorization server to
apply its own matching semantics to the "redirect_uri" value
presented by the client at the authorization endpoint. However, the
OAuth security BCP [OAUTH-SECURITY-TOPICS] as well as the OAuth 2.1
specification [OAUTH-V2] require an authorization server to exactly
match the "redirect_uri" parameter against the set of redirect URIs
previously established for a particular client. This is a means for
early detection of client impersonation attempts and prevents token
leakage and open redirection. As a downside, this can make client
management more cumbersome since the redirect URI is typically the
most volatile part of a client policy.
The exact matching requirement MAY be relaxed when using PAR for
clients that have established authentication credentials with the
authorization server. This is possible since, in contrast to a
conventional authorization request, the authorization server
authenticates the client before the authorization process starts and
thus ensures it is interacting with the legitimate client. The
authorization server MAY allow such clients to specify "redirect_uri"
values that were not previously registered with the authorization
server. This will give the client more flexibility (e.g., to mint
distinct "redirect_uri" values per authorization server at runtime)
and can simplify client management. It is at the discretion of the
authorization server to apply restrictions on supplied "redirect_uri"
values, e.g., the authorization server MAY require a certain URI
prefix or allow only a query parameter to vary at runtime.
| Note: The ability to set up transaction-specific redirect URIs
| is also useful in situations where client IDs and corresponding
| credentials and policies are managed by a trusted third party,
| e.g., via client certificates containing client permissions.
| Such an externally managed client could interact with an
| authorization server trusting the respective third party
| without the need for an additional registration step.
3. The "request" Request Parameter
Clients MAY use the "request" parameter as defined in JAR [RFC9101]
to push a Request Object JWT to the authorization server. The rules
for processing, signing, and encryption of the Request Object as
defined in JAR [RFC9101] apply. Request parameters required by a
given client authentication method are included in the "application/
x-www-form-urlencoded" request directly and are the only parameters
other than "request" in the form body (e.g., mutual TLS client
authentication [RFC8705] uses the "client_id" HTTP request parameter,
while JWT assertion-based client authentication [RFC7523] uses
"client_assertion" and "client_assertion_type"). All other request
parameters, i.e., those pertaining to the authorization request
itself, MUST appear as claims of the JWT representing the
authorization request.
The following is an example of a pushed authorization request using a
signed Request Object with the same authorization request payload as
the example in Section 2.1. The client is authenticated with JWT
client assertion-based authentication [RFC7523] (extra line breaks
and spaces for display purposes only):
POST /as/par HTTP/1.1
Host: as.example.com
Content-Type: application/x-www-form-urlencoded
client_assertion_type=
urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_assertion=eyJraWQiOiJrMmJkYyIsImFsZyI6IlJTMjU2In0.eyJpc3Mi
OiJzNkJoZFJrcXQzIiwic3ViIjoiczZCaGRSa3F0MyIsImF1ZCI6Imh0dHBzOi8vc
2VydmVyLmV4YW1wbGUuY29tIiwiZXhwIjoxNjI1ODY5Njc3fQ.te4IdnP_DK4hWrh
TWA6fyhy3fxlAQZAhfA4lmzRdpoP5uZb-E90R5YxzN1YDA8mnVdpgj_Bx1lG5r6se
f5TlckApA3hahhC804dcqlE4naEmLISmN1pds2WxTMOUzZY8aKKSDzNTDqhyTgE-K
dTb3RafRj7tdZb09zWs7c_moOvfVcQIoy5zz1BvLQKW1Y8JsYvdpu2AvpxRPbcP8W
yeW9B6PL6_fy3pXYKG3e-qUcvPa9kan-mo9EoSgt-YTDQjK1nZMdXIqTluK9caVJE
RWW0fD1Y11_tlOcJn-ya7v7d8YmFyJpkhZfm8x1FoeH0djEicXTixEkdRuzsgUCm6
GQ
&request=eyJraWQiOiJrMmJkYyIsImFsZyI6IlJTMjU2In0.eyJpc3MiOiJzNkJoZ
FJrcXQzIiwiYXVkIjoiaHR0cHM6Ly9zZXJ2ZXIuZXhhbXBsZS5jb20iLCJleHAiOj
E2MjU4Njk2NzcsInJlc3BvbnNlX3R5cGUiOiJjb2RlIiwiY2xpZW50X2lkIjoiczZ
CaGRSa3F0MyIsInJlZGlyZWN0X3VyaSI6Imh0dHBzOi8vY2xpZW50LmV4YW1wbGUu
b3JnL2NiIiwic2NvcGUiOiJhY2NvdW50LWluZm9ybWF0aW9uIiwic3RhdGUiOiJhZ
jBpZmpzbGRraiIsImNvZGVfY2hhbGxlbmdlIjoiSzItbHRjODNhY2M0aDBjOXc2RV
NDX3JFTVRKM2J3dy11Q0hhb2VLMXQ4VSIsImNvZGVfY2hhbGxlbmdlX21ldGhvZCI
6IlMyNTYifQ.l9R3RC9bFBHry_8acObQjEf4fX5yfJkWUPfak3J3iiBm0aaQznPw5
BZ0B3VQZ9_KYdPt5bTkaflS5fSDklM3_7my9MyOSKFYmf46INk6ju_qUuC2crkOQX
ZWYJB-0bnYEbdHpUjazFSUvN49cEGstNQeE-dKDWHNgEojgcuNA_pjKfL9VYp1dEA
6-WjXZ_OlJ7R_mBWpjFAzc0UkQwqX5hfOJoGTqB2tE4a4aB2z8iYlUJp0DeeYp_hP
N6svtmdvte73p5bLGDFpRIlmrBQIAQuxiS0skORpXlS0cBcgHimXVnXOJG7E-A_lS
_5y54dVLQPA1jKYx-fxbYSG7dp2fw
&client_id=s6BhdRkqt3
The authorization server MUST take the following steps beyond the
processing rules defined in Section 2.1:
1. If applicable, decrypt the Request Object as specified in JAR
[RFC9101], Section 6.1.
2. Validate the Request Object signature as specified in JAR
[RFC9101], Section 6.2.
3. If the client has authentication credentials established with the
authorization server, reject the request if the authenticated
"client_id" does not match the "client_id" claim in the Request
Object. Additionally, requiring the "iss" claim to match the
"client_id" is at the discretion of the authorization server.
The following RSA key pair, represented in JSON Web Key (JWK) format
[RFC7517], can be used to validate or recreate the Request Object
signature in the above example (extra line breaks and indentation
within values for display purposes only):
{
"kty": "RSA",
"kid":"k2bdc",
"n": "y9Lqv4fCp6Ei-u2-ZCKq83YvbFEk6JMs_pSj76eMkddWRuWX2aBKGHAtKlE
5P7_vn__PCKZWePt3vGkB6ePgzAFu08NmKemwE5bQI0e6kIChtt_6KzT5Oa
aXDFI6qCLJmk51Cc4VYFaxgqevMncYrzaW_50mZ1yGSFIQzLYP8bijAHGVj
dEFgZaZEN9lsn_GdWLaJpHrB3ROlS50E45wxrlg9xMncVb8qDPuXZarvghL
L0HzOuYRadBJVoWZowDNTpKpk2RklZ7QaBO7XDv3uR7s_sf2g-bAjSYxYUG
sqkNA9b3xVW53am_UZZ3tZbFTIh557JICWKHlWj5uzeJXaw",
"e": "AQAB",
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}
4. Authorization Request
The client uses the "request_uri" value returned by the authorization
server to build an authorization request as defined in [RFC9101].
This is shown in the following example where the client directs the
user agent to make the following HTTP request (extra line breaks and
indentation for display purposes only):
GET /authorize?client_id=s6BhdRkqt3&request_uri=urn%3Aietf%3Aparams
%3Aoauth%3Arequest_uri%3A6esc_11ACC5bwc014ltc14eY22c HTTP/1.1
Host: as.example.com
Since parts of the authorization request content, e.g., the
"code_challenge" parameter value, are unique to a particular
authorization request, the client MUST only use a "request_uri" value
once. Authorization servers SHOULD treat "request_uri" values as
one-time use but MAY allow for duplicate requests due to a user
reloading/refreshing their user agent. An expired "request_uri" MUST
be rejected as invalid.
The authorization server MUST validate authorization requests arising
from a pushed request as it would any other authorization request.
The authorization server MAY omit validation steps that it performed
when the request was pushed, provided that it can validate that the
request was a pushed request and that the request or the
authorization server's policy has not been modified in a way that
would affect the outcome of the omitted steps.
Authorization server policy MAY dictate, either globally or on a per-
client basis, that PAR be the only means for a client to pass
authorization request data. In this case, the authorization server
will refuse, using the "invalid_request" error code, to process any
request to the authorization endpoint that does not have a
"request_uri" parameter with a value obtained from the PAR endpoint.
| Note: Authorization server and clients MAY use metadata as
| defined in Sections 5 and 6 to signal the desired behavior.
5. Authorization Server Metadata
The following authorization server metadata parameters [RFC8414] are
introduced to signal the server's capability and policy with respect
to PAR.
pushed_authorization_request_endpoint
The URL of the pushed authorization request endpoint at which a
client can post an authorization request to exchange for a
"request_uri" value usable at the authorization server.
require_pushed_authorization_requests
Boolean parameter indicating whether the authorization server
accepts authorization request data only via PAR. If omitted, the
default value is "false".
Note that the presence of "pushed_authorization_request_endpoint" is
sufficient for a client to determine that it may use the PAR flow. A
"request_uri" value obtained from the PAR endpoint is usable at the
authorization endpoint regardless of other authorization server
metadata such as "request_uri_parameter_supported" or
"require_request_uri_registration" [OIDC.Disco].
6. Client Metadata
The Dynamic Client Registration Protocol [RFC7591] defines an API for
dynamically registering OAuth 2.0 client metadata with authorization
servers. The metadata defined by [RFC7591], and registered
extensions to it, also imply a general data model for clients that is
useful for authorization server implementations even when the Dynamic
Client Registration Protocol isn't in play. Such implementations
will typically have some sort of user interface available for
managing client configuration. The following client metadata
parameter is introduced by this document to indicate whether pushed
authorization requests are required for the given client.
require_pushed_authorization_requests
Boolean parameter indicating whether the only means of initiating
an authorization request the client is allowed to use is PAR. If
omitted, the default value is "false".
7. Security Considerations
7.1. Request URI Guessing
An attacker could attempt to guess and replay a valid request URI
value and try to impersonate the respective client. The
authorization server MUST account for the considerations given in JAR
[RFC9101], Section 10.2, clause (d) on request URI entropy.
7.2. Open Redirection
An attacker could try to register a redirect URI pointing to a site
under their control in order to obtain authorization codes or launch
other attacks towards the user. The authorization server MUST only
accept new redirect URIs in the pushed authorization request from
authenticated clients.
7.3. Request Object Replay
An attacker could replay a request URI captured from a legitimate
authorization request. In order to cope with such attacks, the
authorization server SHOULD make the request URIs one-time use.
7.4. Client Policy Change
The client policy might change between the lodging of the Request
Object and the authorization request using a particular Request
Object. Therefore, it is recommended that the authorization server
check the request parameter against the client policy when processing
the authorization request.
7.5. Request URI Swapping
An attacker could capture the request URI from one request and then
substitute it into a different authorization request. For example,
in the context of OpenID Connect, an attacker could replace a request
URI asking for a high level of authentication assurance with one that
requires a lower level of assurance. Clients SHOULD make use of PKCE
[RFC7636], a unique "state" parameter [RFC6749], or the OIDC "nonce"
parameter [OIDC] in the pushed Request Object to prevent this attack.
8. Privacy Considerations
OAuth 2.0 is a complex and flexible framework with broad-ranging
privacy implications due to its very nature of having one entity
intermediate user authorization to data access between two other
entities. The privacy considerations of all of OAuth are beyond the
scope of this document, which only defines an alternative way of
initiating one message sequence in the larger framework. However,
using PAR may improve privacy by reducing the potential for
inadvertent information disclosure since it passes the authorization
request data directly between the client and authorization server
over a secure connection in the message body of an HTTP request
rather than in the query component of a URL that passes through the
user agent in the clear.
9. IANA Considerations
9.1. OAuth Authorization Server Metadata
IANA has registered the following values in the IANA "OAuth
Authorization Server Metadata" registry of [IANA.OAuth.Parameters]
established by [RFC8414].
Metadata Name: "pushed_authorization_request_endpoint"
Metadata Description: URL of the authorization server's pushed
authorization request endpoint.
Change Controller: IESG
Specification Document(s): Section 5 of RFC 9126
Metadata Name: "require_pushed_authorization_requests"
Metadata Description: Indicates whether the authorization server
accepts authorization requests only via PAR.
Change Controller: IESG
Specification Document(s): Section 5 of RFC 9126
9.2. OAuth Dynamic Client Registration Metadata
IANA has registered the following value in the IANA "OAuth Dynamic
Client Registration Metadata" registry of [IANA.OAuth.Parameters]
established by [RFC7591].
Client Metadata Name: "require_pushed_authorization_requests"
Client Metadata Description: Indicates whether the client is
required to use PAR to initiate authorization requests.
Change Controller: IESG
Specification Document(s): Section 6 of RFC 9126
9.3. OAuth URI Registration
IANA has registered the following value in the "OAuth URI" registry
of [IANA.OAuth.Parameters] established by [RFC6755].
URN: "urn:ietf:params:oauth:request_uri:"
Common Name: A URN Sub-Namespace for OAuth Request URIs.
Change Controller: IESG
Specification Document(s): Section 2.2 of RFC 9126
10. References
10.1. 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>.
[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>.
[RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", RFC 8414,
DOI 10.17487/RFC8414, June 2018,
<https://www.rfc-editor.org/info/rfc8414>.
[RFC9101] Sakimura, N., Bradley, J., and M. Jones, "The OAuth 2.0
Authorization Framework: JWT-Secured Authorization Request
(JAR)", RFC 9101, DOI 10.17487/RFC9101, August 2021,
<https://www.rfc-editor.org/info/rfc9101>.
10.2. Informative References
[IANA.OAuth.Parameters]
IANA, "OAuth Parameters",
<http://www.iana.org/assignments/oauth-parameters>.
[OAUTH-SECURITY-TOPICS]
Lodderstedt, T., Bradley, J., Labunets, A., and D. Fett,
"OAuth 2.0 Security Best Current Practice", Work in
Progress, Internet-Draft, draft-ietf-oauth-security-
topics-18, 13 April 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-oauth-
security-topics-18>.
[OAUTH-V2] Hardt, D., Parecki, A., and T. Lodderstedt, "The OAuth 2.1
Authorization Framework", Work in Progress, Internet-
Draft, draft-ietf-oauth-v2-1-03, 8 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-oauth-
v2-1-03>.
[OIDC] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0 incorporating
errata set 1", November 2014,
<http://openid.net/specs/openid-connect-core-1_0.html>.
[OIDC.Disco]
Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
Connect Discovery 1.0 incorporating errata set 1",
November 2014, <http://openid.net/specs/openid-connect-
discovery-1_0.html>.
[RFC6755] Campbell, B. and H. Tschofenig, "An IETF URN Sub-Namespace
for OAuth", RFC 6755, DOI 10.17487/RFC6755, October 2012,
<https://www.rfc-editor.org/info/rfc6755>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.
[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>.
[RFC7523] Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token
(JWT) Profile for OAuth 2.0 Client Authentication and
Authorization Grants", RFC 7523, DOI 10.17487/RFC7523, May
2015, <https://www.rfc-editor.org/info/rfc7523>.
[RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
RFC 7591, DOI 10.17487/RFC7591, July 2015,
<https://www.rfc-editor.org/info/rfc7591>.
[RFC7636] Sakimura, N., Ed., Bradley, J., and N. Agarwal, "Proof Key
for Code Exchange by OAuth Public Clients", RFC 7636,
DOI 10.17487/RFC7636, September 2015,
<https://www.rfc-editor.org/info/rfc7636>.
[RFC8252] Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps",
BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017,
<https://www.rfc-editor.org/info/rfc8252>.
[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>.
[RFC8707] Campbell, B., Bradley, J., and H. Tschofenig, "Resource
Indicators for OAuth 2.0", RFC 8707, DOI 10.17487/RFC8707,
February 2020, <https://www.rfc-editor.org/info/rfc8707>.
Acknowledgements
This specification is based on the work on Pushed Request Object
(https://bitbucket.org/openid/fapi/src/master/
Financial_API_Pushed_Request_Object.md) conducted at the Financial-
grade API Working Group at the OpenID Foundation. We would like to
thank the members of the WG for their valuable contributions.
We would like to thank Vladimir Dzhuvinov, Aaron Parecki, Justin
Richer, Sascha Preibisch, Daniel Fett, Michael B. Jones, Annabelle
Backman, Joseph Heenan, Sean Glencross, Maggie Hung, Neil Madden,
Karsten Meyer zu Selhausen, Roman Danyliw, Meral Shirazipour, and
Takahiko Kawasaki for their valuable feedback on this document.
Authors' Addresses
Torsten Lodderstedt
yes.com
Email: torsten@lodderstedt.net
Brian Campbell
Ping Identity
Email: bcampbell@pingidentity.com
Nat Sakimura
NAT.Consulting
Email: nat@sakimura.org
Dave Tonge
Moneyhub Financial Technology
Email: dave@tonge.org
Filip Skokan
Auth0
Email: panva.ip@gmail.com