wdiff rfc9101v1.txt rfc9101.txt

Internet Engineering Task Force (IETF) N. Sakimura
Request for Comments: 9101 NAT.Consulting
Category: Standards Track J. Bradley
ISSN: 2070-1721 Yubico
M. Jones
Microsoft
August 2021

The OAuth 2.0 Authorization Framework: JWT Secured JWT-Secured Authorization Request
(JAR)

Abstract

The authorization request in OAuth 2.0 described in RFC 6749 utilizes
query parameter serialization, which means that authorization request
parameters are encoded in the URI of the request and sent through
user agents such as web browsers. While it is easy to implement, it
means that a) the communication through the user agents is not
integrity protected and thus, the parameters can be tainted, b) the
source of the communication is not authenticated, and c) the
communication through the user agents can be monitored. Because of
these weaknesses, several attacks to the protocol have now been put
forward.

This document introduces the ability to send request parameters in a
JSON Web Token (JWT) instead, which allows the request to be signed
with JSON Web Signature (JWS) and encrypted with JSON Web Encryption
(JWE) so that the integrity, source authentication, and
confidentiality properties of the authorization request are attained.
The request can be sent by value or by reference.

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/rfc9101.

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. Requirements Language
2. Terminology
2.1. Request Object
2.2. Request Object URI
3. Symbols and Abbreviated Terms
4. Request Object
5. Authorization Request
5.1. Passing a Request Object by Value
5.2. Passing a Request Object by Reference
5.2.1. URI Referencing the Request Object
5.2.2. Request Using the "request_uri" Request Parameter
5.2.3. Authorization Server Fetches Request Object
6. Validating JWT-Based Requests
6.1. JWE Encrypted Request Object
6.2. JWS-Signed Request Object
6.3. Request Parameter Assembly and Validation
7. Authorization Server Response
8. TLS Requirements
9. IANA Considerations
9.1. OAuth Parameters Registration
9.2. OAuth Authorization Server Metadata Registry
9.3. OAuth Dynamic Client Registration Metadata Registry
9.4. Media Type Registration
9.4.1. Registry Contents
10. Security Considerations
10.1. Choice of Algorithms
10.2. Request Source Authentication
10.3. Explicit Endpoints
10.4. Risks Associated with request_uri
10.4.1. DDoS Attack on the Authorization Server
10.4.2. Request URI Rewrite
10.5. Downgrade Attack
10.6. TLS Security Considerations
10.7. Parameter Mismatches
10.8. Cross-JWT Confusion
11. Privacy Considerations
11.1. Collection Limitation
11.2. Disclosure Limitation
11.2.1. Request Disclosure
11.2.2. Tracking Using Request Object URI
12. References
12.1. Normative References
12.2. Informative References
Acknowledgements
Authors' Addresses

1. Introduction

The authorization request in OAuth 2.0 [RFC6749] utilizes query
parameter serialization and is typically sent through user agents
such as web browsers.

For example, the parameters "response_type", "client_id", "state",
and "redirect_uri" are encoded in the URI of the request:

GET /authorize?response_type=code&client_id=s6BhdRkqt3&state=xyz
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com

While it is easy to implement, the encoding in the URI does not allow
application-layer security to be used to provide confidentiality and
integrity protection. While TLS is used to offer communication
security between the client and the user-agent user agent as well as the user- user
agent and the authorization server, TLS sessions are terminated in
the user-agent. user agent. In addition, TLS sessions may be terminated
prematurely at some middlebox (such as a load balancer).

As a result, the authorization request of [RFC6749] has shortcomings
in that:

(a) the communication through the user agents is not integrity
protected, and thus, the parameters can be tainted (integrity
protection failure);

(b) the source of the communication is not authenticated (source
authentication failure);

Due to these inherent weaknesses, several attacks against the
protocol, such as redirection URI rewriting, have been identified.

The use of application-layer security mitigates these issues.

The use of application-layer security allows requests to be prepared
by a trusted third party so that a client application cannot request
more permissions than previously agreed upon.

Furthermore, passing the request by reference allows the reduction of
over-the-wire overhead.

The JWT [RFC7519] encoding has been chosen because of:

(1) its close relationship with JSON, which is used as OAuth's
response format

(2) its developer friendliness due to its textual nature

(3) its relative compactness compared to XML

(4) its development status as a Proposed Standard, along with the
associated signing and encryption methods [RFC7515] [RFC7516]

(5) the relative ease of JWS and JWE compared to XML Signature and
Encryption.

The parameters "request" and "request_uri" are introduced as
additional authorization request parameters for the OAuth 2.0
[RFC6749] flows. The "request" parameter is a JSON Web Token (JWT)
[RFC7519] whose JWT Claims Set holds the JSON-encoded OAuth 2.0
authorization request parameters. Note that, in contrast to RFC
7519, the elements of the Claims Set are encoded OAuth request
parameters [IANA.OAuth.Parameters], supplemented with only a few of
the IANA-managed JSON Web Token Claims [IANA.JWT.Claims], in
particular, "iss" and "aud". The JWT in the "request" parameter is
integrity protected and source authenticated using JWS.

The JWT [RFC7519] can be passed to the authorization endpoint by
reference, in which case the parameter "request_uri" is used instead
of "request".

Using JWT [RFC7519] as the request encoding instead of query
parameters has several advantages:

(a) Integrity protection. The request can be signed so that the
integrity of the request can be checked.

(b) Source authentication. The request can be signed so that the
signer can be authenticated.

(c) Confidentiality protection. The request can be encrypted so
that end-to-end confidentiality can be provided even if the TLS
connection is terminated at one point or another (including at
and before user-agents). user agents).

(d) Collection minimization. The request can be signed by a trusted
third party attesting that the authorization request is
compliant with a certain policy. For example, a request can be
pre-examined by a trusted third party to confirm that all the
personal data requested is strictly necessary to perform the
process that the end user asked for; the request would then be
signed by that trusted third party. The authorization server
then examines the signature and shows the conformance status to
the end user who would have some assurance as to the legitimacy
of the request when authorizing it. In some cases, it may even
be desirable to skip the authorization dialogue under such
circumstances.

There are a few cases where request by reference is useful, such as:

1. when it is desirable to reduce the size of a transmitted request.
The use of application-layer security increases the size of the
request particularly when public-key cryptography is used.

2. when the client does not want to do the application-level
cryptography. The authorization server may provide an endpoint
to accept the authorization request through direct communication
with the client, so that the client is authenticated and the
channel is TLS protected.

This capability is in use by OpenID Connect [OpenID.Core].

1.1. Requirements Language

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.

2. Terminology

For the purposes of this specification, the following terms and
definitions apply in addition to what is defined in OAuth 2.0
Framework [RFC6749], JSON Web Signature [RFC7515], and JSON Web
Encryption [RFC7516].

2.1. Request Object

A Request Object is a JSON Web Token (JWT) [RFC7519] whose JWT Claims
Set holds the JSON-encoded OAuth 2.0 authorization request
parameters.

2.2. Request Object URI

A Request Object URI is an absolute URI that references the set of
parameters comprising an OAuth 2.0 authorization request. The
content of the resource referenced by the URI is a Request Object
(Section 2.1), unless the URI was provided to the client by the same
authorization server, in which case the content is an implementation
detail at the discretion of the authorization server. The former content
being a Request Object is to ensure interoperability in cases where
the provider of the "request_uri" is a separate entity from the
consumer, such as when a client provides a URI referencing a Request
Object stored on the client's backend service that is made accessible
via HTTPS. In the latter case, where the authorization server is
both provider and consumer of the URI, such as when it offers an
endpoint that provides a URI in exchange for a Request Object, this
interoperability concern does not apply.

3. Symbols and Abbreviated Terms

The following abbreviations are common to this specification.

JSON: JavaScript Object Notation

JWT: JSON Web Token

JWS: JSON Web Signature

JWE: JSON Web Encryption

URI: Uniform Resource Identifier

URL: Uniform Resource Locator

4. Request Object

A Request Object (Section 2.1) is used to provide authorization
request parameters for an OAuth 2.0 authorization request. It MUST
contain all the parameters (including extension parameters) used to
process the OAuth 2.0 [RFC6749] authorization request except the
"request" and "request_uri" parameters that are defined in this
document. The parameters are represented as the JWT Claims of the
object. Parameter names and string values MUST be included as JSON
strings. Since Request Objects are handled across domains and
potentially outside of a closed ecosystem, per Section 8.1 of
[RFC8259], these JSON strings MUST be encoded using UTF-8 [RFC3629].
Numerical values MUST be included as JSON numbers. The Request
Object MAY include any extension parameters. This JSON [RFC8259]
object constitutes the JWT Claims Set defined in JWT [RFC7519]. The
JWT Claims Set is then signed or signed and encrypted.

To sign, JSON Web Signature (JWS) [RFC7515] is used. The result is a
JWS-signed JWT [RFC7519]. If signed, the Authorization Request
Object SHOULD contain the Claims "iss" (issuer) and "aud" (audience)
as members with their semantics being the same as defined in the JWT
[RFC7519] specification. The value of "aud" should be the value of
the authorization server (AS) "issuer", as defined in RFC 8414
[RFC8414].

To encrypt, JWE [RFC7516] is used. When both signature and
encryption are being applied, the JWT MUST be signed, then encrypted,
as described in Section 11.2 of [RFC7519]. The result is a Nested
JWT, as defined in [RFC7519].

The client determines the algorithms used to sign and encrypt Request
Objects. The algorithms chosen need to be supported by both the
client and the authorization server. The client can inform the
authorization server of the algorithms that it supports in its
dynamic client registration metadata [RFC7591], specifically, the
metadata values "request_object_signing_alg",
"request_object_encryption_alg", and "request_object_encryption_enc".
Likewise, the authorization server can inform the client of the
algorithms that it supports in its authorization server metadata
[RFC8414], specifically, the metadata values
"request_object_signing_alg_values_supported",
"request_object_encryption_alg_values_supported", and
"request_object_encryption_enc_values_supported".

The Request Object MAY be sent by value, as described in Section 5.1,
or by reference, as described in Section 5.2. "request" and
"request_uri" parameters MUST NOT be included in Request Objects.

A Request Object (Section 2.1) has the media type [RFC2046]
"application/oauth-authz-req+jwt". Note that some existing
deployments may alternatively be using the type "application/jwt".

The following is an example of the Claims in a Request Object before
base64url [RFC7515] encoding and signing. Note that it includes the
extension parameters "nonce" and "max_age".

{
"iss": "s6BhdRkqt3",
"aud": "https://server.example.com",
"response_type": "code id_token",
"client_id": "s6BhdRkqt3",
"redirect_uri": "https://client.example.org/cb",
"scope": "openid",
"state": "af0ifjsldkj",
"nonce": "n-0S6_WzA2Mj",
"max_age": 86400
}

Signing it with the "RS256" algorithm [RFC7518] results in this
Request Object value (with line wraps within values for display
purposes only):

eyJhbGciOiJSUzI1NiIsImtpZCI6ImsyYmRjIn0.ewogICAgImlzcyI6ICJzNkJoZF
JrcXQzIiwKICAgICJhdWQiOiAiaHR0cHM6Ly9zZXJ2ZXIuZXhhbXBsZS5jb20iLAog
ICAgInJlc3BvbnNlX3R5cGUiOiAiY29kZSBpZF90b2tlbiIsCiAgICAiY2xpZW50X2
lkIjogInM2QmhkUmtxdDMiLAogICAgInJlZGlyZWN0X3VyaSI6ICJodHRwczovL2Ns
aWVudC5leGFtcGxlLm9yZy9jYiIsCiAgICAic2NvcGUiOiAib3BlbmlkIiwKICAgIC
JzdGF0ZSI6ICJhZjBpZmpzbGRraiIsCiAgICAibm9uY2UiOiAibi0wUzZfV3pBMk1q
IiwKICAgICJtYXhfYWdlIjogODY0MDAKfQ.Nsxa_18VUElVaPjqW_ToI1yrEJ67BgK
b5xsuZRVqzGkfKrOIX7BCx0biSxYGmjK9KJPctH1OC0iQJwXu5YVY-vnW0_PLJb1C2
HG-ztVzcnKZC2gE4i0vgQcpkUOCpW3SEYXnyWnKzuKzqSb1wAZALo5f89B_p6QA6j6
JwBSRvdVsDPdulW8lKxGTbH82czCaQ50rLAg3EYLYaCb4ik4I1zGXE4fvim9FIMs8O
CMmzwIB5S-ujFfzwFjoyuPEV4hJnoVUmXR_W9typPf846lGwA8h9G9oNTIuX8Ft2jf
pnZdFmLg3_wr3Wa5q3a-lfbgF3S9H_8nN3j1i7tLR_5Nz-g

The following RSA public key, represented in JSON Web Key (JWK)
format, can be used to validate the Request Object signature in this
and subsequent Request Object examples (with line wraps within values
for display purposes only):

{
"kty":"RSA",
"kid":"k2bdc",
"n":"x5RbkAZkmpRxia65qRQ1wwSMSxQUnS7gcpVTV_cdHmfmG2ltd2yabEO9XadD8
pJNZubINPpmgHh3J1aD9WRwS05ucmFq3CfFsluLt13_7oX5yDRSKX7poXmT_5
ko8k4NJZPMAO8fPToDTH7kHYbONSE2FYa5GZ60CUsFhSonI-dcMDJ0Ary9lxI
w5k2z4TAdARVWcS7sD07VhlMMshrwsPHBQgTatlkxyIHXbYdtak8fqvNAwr7O
lVEvM_Ipf5OfmdB8Sd-wjzaBsyP4VhJKoi_qdgSzpC694XZeYPq45Sw-q51iF
UlcOlTCI7z6jltUtnR6ySn6XDGFnzH5Fe5ypw",
"e":"AQAB"
}

5. Authorization Request

The client constructs the authorization request URI by adding the
following parameters to the query component of the authorization
endpoint URI using the "application/x-www-form-urlencoded" format:

request
REQUIRED unless "request_uri" is specified. The Request Object
(Section 2.1) that holds authorization request parameters stated
in Section 4 of [RFC6749] (OAuth 2.0). If this parameter is
present in the authorization request, "request_uri" MUST NOT be
present.

request_uri
REQUIRED unless "request" is specified. The absolute URI, as
defined by RFC 3986 [RFC3986], that is the Request Object URI
(Section 2.2) referencing the authorization request parameters
stated in Section 4 of [RFC6749] (OAuth 2.0). If this parameter
is present in the authorization request, "request" MUST NOT be
present.

client_id
REQUIRED. OAuth 2.0 [RFC6749] "client_id". The value MUST match
the "request" or "request_uri" Request Object's (Section 2.1)
"client_id".

The client directs the resource owner to the constructed URI using an
HTTP redirection response or by other means available to it via the
user-agent.
user agent.

For example, the client directs the end user's user-agent user agent to make the
following HTTPS request:

GET /authz?client_id=s6BhdRkqt3&request=eyJhbG..AlMGzw HTTP/1.1
Host: server.example.com

The value for the request parameter is abbreviated for brevity.

The Authorization Request Object MUST be one of the following:

(a) JWS signed

(b) JWS signed and JWE encrypted

The client MAY send the parameters included in the Request Object
duplicated in the query parameters as well for backward
compatibility, etc. However, the authorization server supporting
this specification MUST only use the parameters included in the
Request Object.

5.1. Passing a Request Object by Value

The client sends the authorization request as a Request Object to the
authorization endpoint as the "request" parameter value.

The following is an example of an authorization request using the
"request" parameter (with line wraps within values for display
purposes only):

https://server.example.com/authorize?client_id=s6BhdRkqt3&
request=eyJhbGciOiJSUzI1NiIsImtpZCI6ImsyYmRjIn0.ewogICAgImlzcyI6
ICJzNkJoZFJrcXQzIiwKICAgICJhdWQiOiAiaHR0cHM6Ly9zZXJ2ZXIuZXhhbXBs
ZS5jb20iLAogICAgInJlc3BvbnNlX3R5cGUiOiAiY29kZSBpZF90b2tlbiIsCiAg
ICAiY2xpZW50X2lkIjogInM2QmhkUmtxdDMiLAogICAgInJlZGlyZWN0X3VyaSI6
ICJodHRwczovL2NsaWVudC5leGFtcGxlLm9yZy9jYiIsCiAgICAic2NvcGUiOiAi
b3BlbmlkIiwKICAgICJzdGF0ZSI6ICJhZjBpZmpzbGRraiIsCiAgICAibm9uY2Ui
OiAibi0wUzZfV3pBMk1qIiwKICAgICJtYXhfYWdlIjogODY0MDAKfQ.Nsxa_18VU
ElVaPjqW_ToI1yrEJ67BgKb5xsuZRVqzGkfKrOIX7BCx0biSxYGmjK9KJPctH1OC
0iQJwXu5YVY-vnW0_PLJb1C2HG-ztVzcnKZC2gE4i0vgQcpkUOCpW3SEYXnyWnKz
uKzqSb1wAZALo5f89B_p6QA6j6JwBSRvdVsDPdulW8lKxGTbH82czCaQ50rLAg3E
YLYaCb4ik4I1zGXE4fvim9FIMs8OCMmzwIB5S-ujFfzwFjoyuPEV4hJnoVUmXR_W
9typPf846lGwA8h9G9oNTIuX8Ft2jfpnZdFmLg3_wr3Wa5q3a-lfbgF3S9H_8nN3
j1i7tLR_5Nz-g

5.2. Passing a Request Object by Reference

The "request_uri" authorization request parameter enables OAuth
authorization requests to be passed by reference rather than by
value. This parameter is used identically to the "request"
parameter, except that the Request Object value is retrieved from the
resource identified by the specified URI rather than passed by value.

The entire Request URI SHOULD NOT exceed 512 ASCII characters. There
are two reasons for this restriction:

1. Many phones on the market as of this writing still do not accept
large payloads. The restriction is typically either 512 or 1024
ASCII characters.

2. On a slow connection such as a 2G mobile connection, a large URL
would cause a slow response; therefore, the use of such is not
advisable from the user-experience point of view.

The contents of the resource referenced by the "request_uri" MUST be
a Request Object and MUST be reachable by the authorization server
unless the URI was provided to the client by the authorization
server. In the first case, the "request_uri" MUST be an "https" URI,
as specified in Section 2.7.2 of [RFC7230]. In the second case, it
MUST be a URN, as specified in [RFC8141].

The following is an example of the contents of a Request Object
resource that can be referenced by a "request_uri" (with line wraps
within values for display purposes only):

5.2.1. URI Referencing the Request Object

The client stores the Request Object resource either locally or
remotely at a URI the authorization server can access. Such a
facility may be provided by the authorization server or a trusted
third party. For example, the authorization server may provide a URL
to which the client POSTs the Request Object and obtains the Request
URI. This URI is the Request Object URI, "request_uri".

It is possible for the Request Object to include values that are to
be revealed only to the authorization server. As such, the
"request_uri" MUST have appropriate entropy for its lifetime so that
the URI is not guessable if publicly retrievable. For the guidance,
refer to Section 5.1.4.2.2 of [RFC6819] and "Good Practices for
Capability URLs" [CapURLs]. It is RECOMMENDED that the "request_uri"
be removed after a reasonable timeout unless access control measures
are taken.

The following is an example of a Request Object URI value (with line
wraps within values for display purposes only). In this example, a
trusted third-party service hosts the Request Object.

https://tfp.example.org/request.jwt/
GkurKxf5T0Y-mnPFCHqWOMiZi4VS138cQO_V7PZHAdM

5.2.2. Request Using the "request_uri" Request Parameter

The client sends the authorization request to the authorization
endpoint.

The following is an example of an authorization request using the
"request_uri" parameter (with line wraps within values for display
purposes only):

https://server.example.com/authorize?
client_id=s6BhdRkqt3
&request_uri=https%3A%2F%2Ftfp.example.org%2Frequest.jwt
%2FGkurKxf5T0Y-mnPFCHqWOMiZi4VS138cQO_V7PZHAdM

5.2.3. Authorization Server Fetches Request Object

Upon receipt of the Request, the authorization server MUST send an
HTTP "GET" request to the "request_uri" to retrieve the referenced
Request Object unless it the Request Object is stored in a way so that it
the server can retrieve it through other mechanisms securely and
parse it to recreate the authorization request parameters.

The following is an example of this fetch process. In this example,
a trusted third-party service hosts the Request Object.

GET /request.jwt/GkurKxf5T0Y-mnPFCHqWOMiZi4VS138cQO_V7PZHAdM HTTP/1.1
Host: tfp.example.org

The following is an example of the fetch response:

HTTP/1.1 200 OK
Date: Thu, 20 Aug 2020 23:52:39 GMT
Server: Apache/2.4.43 (tfp.example.org)
Content-type: application/oauth-authz-req+jwt
Content-Length: 797
Last-Modified: Wed, 19 Aug 2020 23:52:32 GMT

6. Validating JWT-Based Requests

6.1. JWE Encrypted Request Object

If the Request Object is encrypted, the authorization server MUST
decrypt the JWT in accordance with the JSON Web Encryption [RFC7516]
specification.

The result is a signed Request Object.

If decryption fails, the authorization server MUST return an
"invalid_request_object" error to the client in response to the
authorization request.

6.2. JWS-Signed Request Object

The authorization server MUST validate the signature of the JWS-
signed [RFC7515] Request Object. If a "kid" Header Parameter is
present, the key identified MUST be the key used and MUST be a key
associated with the client. The signature MUST be validated using a
key associated with the client and the algorithm specified in the
"alg" Header Parameter. Algorithm verification MUST be performed, as
specified in Sections 3.1 and 3.2 of [RFC8725].

If the key is not associated with the client or if signature
validation fails, the authorization server MUST return an
"invalid_request_object" error to the client in response to the
authorization request.

6.3. Request Parameter Assembly and Validation

The authorization server MUST extract the set of authorization
request parameters from the Request Object value. The authorization
server MUST only use the parameters in the Request Object, even if
the same parameter is provided in the query parameter. The client ID
values in the "client_id" request parameter and in the Request Object
"client_id" claim MUST be identical. The authorization server then
validates the request, as specified in OAuth 2.0 [RFC6749].

If the Client ID check or the request validation fails, then the
authorization server MUST return an error to the client in response
to the authorization request, as specified in Section 5.2 of
[RFC6749] (OAuth 2.0).

7. Authorization Server Response

The authorization server response is created and sent to the client
as in Section 4 of [RFC6749] (OAuth 2.0).

In addition, this document uses these additional error values:

invalid_request_uri
The "request_uri" in the authorization request returns an error or
contains invalid data.

invalid_request_object
The request parameter contains an invalid Request Object.

request_not_supported
The authorization server does not support the use of the "request"
parameter.

request_uri_not_supported
The authorization server does not support the use of the
"request_uri" parameter.

8. TLS Requirements

Client implementations supporting the Request Object URI method MUST
support TLS, following "Recommendations for Secure Use of Transport
Layer Security (TLS) and Datagram Transport Layer Security (DTLS)"
[RFC7525].

To protect against information disclosure and tampering,
confidentiality protection MUST be applied using TLS with a cipher
suite that provides confidentiality and integrity protection.

HTTP clients MUST also verify the TLS server certificate, using DNS-
ID [RFC6125], to avoid man-in-the-middle attacks. The rules and
guidelines defined in [RFC6125] apply here, with the following
considerations:

* Support for DNS-ID identifier type (that is, the dNSName identity
in the subjectAltName extension) is REQUIRED. Certification
authorities that issue server certificates MUST support the DNS-ID
identifier type, and the DNS-ID identifier type MUST be present in
server certificates.

* DNS names in server certificates MAY contain the wildcard
character "*".

* Clients MUST NOT use CN-ID identifiers; a Common Name field (CN
field) may be present in the server certificate's subject name but
MUST NOT be used for authentication within the rules described in
[RFC7525].

* SRV-ID and URI-ID as described in Section 6.5 of [RFC6125] MUST
NOT be used for comparison.

9. IANA Considerations

9.1. OAuth Parameters Registration

Since the Request Object is a JWT, the core JWT claims cannot be used
for any purpose in the Request Object other than for what JWT
dictates. Thus, they have been registered as OAuth authorization
request parameters to avoid future OAuth extensions using them with
different meanings.

This specification adds the following values to the "OAuth
Parameters" registry [IANA.OAuth.Parameters] established by
[RFC6749].

Name: "iss"
Parameter Usage Location: authorization request
Change Controller: IETF
Specification Document(s): This document and Section 4.1.1 of
[RFC7519].

Name: "sub"
Parameter Usage Location: authorization request
Change Controller: IETF
Specification Document(s): This document and Section 4.1.2 of
[RFC7519].

Name: "aud"
Parameter Usage Location: authorization request
Change Controller: IETF
Specification Document(s): This document and Section 4.1.3 of
[RFC7519].

Name: "exp"
Parameter Usage Location: authorization request
Change Controller: IETF
Specification Document(s): This document and Section 4.1.4 of
[RFC7519].

Name: "nbf"
Parameter Usage Location: authorization request
Change Controller: IETF
Specification Document(s): This document and Section 4.1.5 of
[RFC7519].

Name: "iat"
Parameter Usage Location: authorization request
Change Controller: IETF
Specification Document(s): This document and Section 4.1.6 of
[RFC7519].

Name: "jti"
Parameter Usage Location: authorization request
Change Controller: IETF
Specification Document(s): This document and Section 4.1.7 of
[RFC7519].

9.2. OAuth Authorization Server Metadata Registry

This specification adds the following value to the "OAuth
Authorization Server Metadata" registry [IANA.OAuth.Parameters]
established by [RFC8414].

Metadata Name: "require_signed_request_object"
Metadata Description: Indicates where authorization request needs to
be protected as Request Object and provided through either
"request" or "request_uri parameter".
Change Controller: IETF
Specification Document(s): Section 10.5 of this document.

9.3. OAuth Dynamic Client Registration Metadata Registry

This specification adds the following value to the "OAuth Dynamic
Client Registration Metadata" registry [IANA.OAuth.Parameters]
established by [RFC7591].

9.4. Media Type Registration

9.4.1. Registry Contents

This section registers the "application/oauth-authz-req+jwt" media
type [RFC2046] in the "Media Types" registry [IANA.MediaTypes] in the
manner described in [RFC6838]. It can be used to indicate that the
content is a JWT containing Request Object claims.

Type name: application
Subtype name: oauth-authz-req+jwt
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary; a Request Object is a JWT; JWT
values are encoded as a series of base64url-encoded values (some
of which may be the empty string) separated by period (".")
characters.
Security considerations: See Section 10 of RFC 9101
Interoperability considerations: N/A
Published specification: Section 4 of RFC 9101
Applications that use this media type: Applications that use Request
Objects to make an OAuth 2.0 authorization request
Fragment identifier considerations: N/A
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A
Person & email address to contact for further information:
Nat Sakimura <nat@nat.consulting>
Intended usage: COMMON
Restrictions on usage: none
Author: Nat Sakimura <nat@nat.consulting>
Change controller: IETF
Provisional registration? No

10. Security Considerations

In addition to all the security considerations discussed in OAuth 2.0
[RFC6819], the security considerations in [RFC7515], [RFC7516],
[RFC7518], and [RFC8725] need to be considered. Also, there are
several academic papers such as [BASIN] that provide useful insight
into the security properties of protocols like OAuth.

In consideration of the above, this document advises taking the
following security considerations into account.

10.1. Choice of Algorithms

When sending the Authorization Request Object through the "request"
parameter, it MUST be either signed using JWS [RFC7515] or signed and
then encrypted using JWS [RFC7515] and JWE [RFC7516], respectively,
with algorithms considered appropriate at the time.

10.2. Request Source Authentication

The source of the authorization request MUST always be verified.
There are several ways to do it:

(a) Verifying the JWS Signature of the Request Object.

(b) Verifying that the symmetric key for the JWE encryption is the
correct one if the JWE is using symmetric encryption. Note,
however, that if public key encryption is used, no source
authentication is enabled by the encryption, as any party can
encrypt to the public key.

(c) Verifying the TLS Server Identity of the Request Object URI. In
this case, the authorization server MUST know out-of-band that
the client uses the Request Object URI and only the client is
covered by the TLS certificate. In general, this is not a
reliable method.

(d) When an authorization server implements a service that returns a
Request Object URI in exchange for a Request Object, the
authorization server MUST perform client authentication to
accept the Request Object and bind the client identifier to the
Request Object URI it is providing. It MUST validate the
signature, per (a). Since the Request Object URI can be
replayed, the lifetime of the Request Object URI MUST be short
and preferably one-time use. The entropy of the Request Object
URI MUST be sufficiently large. The adequate shortness of the
validity and the entropy of the Request Object URI depends on
the risk calculation based on the value of the resource being
protected. A general guidance for the validity time would be
less than a minute, and the Request Object URI is to include a
cryptographic random value of 128 bits or more at the time of
the writing of this specification.

(e) When a trusted third-party service returns a Request Object URI
in exchange for a Request Object, it MUST validate the
signature, per (a). In addition, the authorization server MUST
be trusted by the third-party service and MUST know out-of-band
that the client is also trusted by it.

10.3. Explicit Endpoints

Although this specification does not require them, research such as
[BASIN] points out that it is a good practice to explicitly state the
intended interaction endpoints and the message position in the
sequence in a tamper-evident manner so that the intent of the
initiator is unambiguous. It is RECOMMENDED by this specification to
use this practice for the following endpoints defined in [RFC6749],
[RFC6750], and [RFC8414]:

(a) Protected resources ("protected_resources")

(b) Authorization endpoint ("authorization_endpoint")

(d) Token endpoint ("token_endpoint")

Further, if dynamic discovery is used, then this practice also
applies to the discovery-related endpoints.

In [RFC6749], while the redirection URI is included in the
authorization request, others are not. As a result, the same applies
to the Authorization Request Object.

10.4. Risks Associated with request_uri

The introduction of "request_uri" introduces several attack
possibilities. Consult the security considerations in Section 7 of
[RFC3986] for more information regarding risks associated with URIs.

10.4.1. DDoS Attack on the Authorization Server

A set of malicious clients can launch a DoS attack to the
authorization server by pointing the "request_uri" to a URI that
returns extremely large content or is extremely slow to respond.
Under such an attack, the server may use up its resource and start
failing.

Similarly, a malicious client can specify a "request_uri" value that
itself points to an authorization request URI that uses "request_uri"
to cause the recursive lookup.

To prevent such an attack from succeeding, the server should a) check
that the value of the "request_uri" parameter does not point to an
unexpected location, b) check that the media type of the response is
"application/oauth-authz-req+jwt", c) implement a timeout for
obtaining the content of "request_uri", and d) not perform recursive
GET on the "request_uri".

10.4.2. Request URI Rewrite

The value of "request_uri" is not signed; thus, it can be tampered
with by a man-in-the-browser attacker. Several attack possibilities
arise because of this. For example, a) an attacker may create
another file that the rewritten URI points to, making it possible to
request extra scope, or b) an attacker may launch a DoS attack on a
victim site by setting the value of "request_uri" to be that of the
victim.

To prevent such an attack from succeeding, the server should a) check
that the value of the "request_uri" parameter does not point to an
unexpected location, b) check that the media type of the response is
"application/oauth-authz-req+jwt", and c) implement a timeout for
obtaining the content of "request_uri".

10.5. Downgrade Attack

Unless the protocol used by the client and the server is locked down
to use an OAuth JWT Secured JWT-Secured Authorization Request (JAR), it is
possible for an attacker to use RFC 6749 requests to bypass all the
protection provided by this specification.

To prevent this kind of attack, this specification defines a new client
metadata and server metadata, metadata values, both named
"require_signed_request_object", whose value is a boolean. values are both booleans.

When the value of it as client metadata is "true", then the server
MUST reject the authorization request from the client that does not
conform to this specification. It MUST also reject the request if
the Request Object uses "alg":"none" an "alg" value of "none" when this server
metadata value is "true". If omitted, the default value is "false".

When the value of it as server metadata is "true", then the server
MUST reject the authorization request from any client that does not
conform to this specification. It MUST also reject the request if
the Request Object uses "alg":"none". an "alg" value of "none". If omitted, the
default value is "false".

Note that even if "require_signed_request_object" metadata values are
not present, the client MAY use signed Request Objects, provided that
there are signing algorithms mutually supported by the client and the
server. Use of signing algorithm metadata is described in Section 4.

10.6. TLS Security Considerations

Current security considerations can be found in "Recommendations for
Secure Use of Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)" [RFC7525]. This supersedes the TLS version
recommendations in OAuth 2.0 [RFC6749].

10.7. Parameter Mismatches

Given that OAuth parameter values are being sent in two different
places, as normal OAuth parameters and as Request Object claims,
implementations must guard against attacks that could use mismatching
parameter values to obtain unintended outcomes. That is the reason
that the two client ID values MUST match, the reason that only the
parameter values from the Request Object are to be used, and the
reason that neither "request" nor "request_uri" can appear in a
Request Object.

10.8. Cross-JWT Confusion

As described in Section 2.8 of [RFC8725], attackers may attempt to
use a JWT issued for one purpose in a context that it was not
intended for. The mitigations described for these attacks can be
applied to Request Objects.

One way that an attacker might attempt to repurpose a Request Object
is to try to use it as a client authentication JWT, as described in
Section 2.2 of [RFC7523]. A simple way to prevent this is to never
use the client ID as the "sub" value in a Request Object.

Another way to prevent cross-JWT confusion is to use explicit typing,
as described in Section 3.11 of [RFC8725]. One would explicitly type
a Request Object by including a "typ" Header Parameter with the value
"oauth-authz-req+jwt" (which is registered in Section 9.4.1). Note,
however, that requiring explicitly typed Request Objects at existing
authorization servers will break most existing deployments, as
existing clients are already commonly using untyped Request Objects,
especially with OpenID Connect [OpenID.Core]. However, requiring
explicit typing would be a good idea for new OAuth deployment
profiles where compatibility with existing deployments is not a
consideration.

Finally, yet another way to prevent cross-JWT confusion is to use a
key management regime in which keys used to sign Request Objects are
identifiably distinct from those used for other purposes. Then, if
an adversary attempts to repurpose the Request Object in another
context, a key mismatch will occur occur, thwarting the attack.

11. Privacy Considerations

When the client is being granted access to a protected resource
containing personal data, both the client and the authorization
server need to adhere to Privacy Principles. "Privacy Considerations
for Internet Protocols" [RFC6973] gives excellent guidance on the
enhancement of protocol design and implementation. The provisions
listed in it should be followed.

Most of the provisions would apply to "The OAuth 2.0 Authorization
Framework" [RFC6749] and "The OAuth 2.0 Authorization Framework:
Bearer Token Usage" [RFC6750] and are not specific to this
specification. In what follows, only the provisions specific to this
specification are noted.

11.1. Collection Limitation

When the client is being granted access to a protected resource
containing personal data, the client SHOULD limit the collection of
personal data to that which is within the bounds of applicable law
and strictly necessary for the specified purpose(s).

It is often hard for the user to find out if the personal data asked
for is strictly necessary. A trusted third-party service can help
the user by examining the client request, comparing it to the
proposed processing by the client, and certifying the request. After
the certification, the client, when making an authorization request,
can submit an authorization request to the trusted third-party
service to obtain the Request Object URI. This process has two
steps:

(1) (Certification Process) The trusted third-party service examines
the business process of the client and determines what claims
they need; this is the certification process. Once the client
is certified, they are issued a client credential to
authenticate against to push Request Objects to the trusted
third-party service to get the "request_uri".

(2) (Translation Process) The client uses the client credential that
it got to push the Request Object to the trusted third-party
service to get the "request_uri". The trusted third-party
service also verifies that the Request Object is consistent with
the claims that the client is eligible for for, per the prior step.

Upon receiving such a Request Object URI in the authorization
request, the authorization server first verifies that the authority
portion of the Request Object URI is a legitimate one for the trusted
third-party service. Then, the authorization server issues an HTTP
GET request to the Request Object URI. Upon connecting, the
authorization server MUST verify that the server identity represented
in the TLS certificate is legitimate for the Request Object URI.
Then, the authorization server can obtain the Request Object, which
includes the "client_id" representing the client.

The Consent screen MUST indicate the client and SHOULD indicate that
the request has been vetted by the trusted third-party service for
the adherence to the Collection Limitation collection limitation principle.

11.2. Disclosure Limitation

11.2.1. Request Disclosure

This specification allows extension parameters. These may include
potentially sensitive information. Since URI query parameters may
leak through various means but most notably through referrer and
browser history, if the authorization request contains a potentially
sensitive parameter, the client SHOULD encrypt the Request Object
using JWE [RFC7516].

Where the Request Object URI method is being used, if the Request
Object contains personally identifiable or sensitive information, the
"request_uri" SHOULD be used only once and have a short validity
period, and it MUST have large enough sufficient entropy deemed necessary with for the applicable
security policy policies unless the Request Object itself is encrypted using
JWE
[RFC7516] encrypted. [RFC7516]. The adequate shortness of the validity and the
entropy of the Request Object URI depends on the risk calculation
based on the value of the resource being protected. A general
guidance for the validity time would be less than a minute, and the
Request Object URI is to include a cryptographic random value of 128
bits or more at the time of the writing of this specification.

11.2.2. Tracking Using Request Object URI

Even if the protected resource does not include personally
identifiable information, it is sometimes possible to identify the
user through the Request Object URI if persistent static per-user
Request Object URIs are used. A third party may observe it through
browser history, etc. and start correlating the user's activity using
it. In a way, it is a data disclosure as well and should be avoided.

Therefore, per-user persistent Request Object URIs should be avoided.
Single-use Request Object URIs are one alternative.

12. References

12.1. Normative References

[IANA.MediaTypes]
IANA, "Media Types",
<https://www.iana.org/assignments/media-types>.

[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>.

[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.

[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>.

[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.

[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>.

[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.

[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>.

[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, DOI 10.17487/RFC7516, May 2015,
<https://www.rfc-editor.org/info/rfc7516>.

[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/info/rfc7518>.

[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>.

[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.

[RFC8141] Saint-Andre, P. and J. Klensin, "Uniform Resource Names
(URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017,
<https://www.rfc-editor.org/info/rfc8141>.

[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>.

12.2. Informative References

[BASIN] Basin, D., Cremers, C., and S. Meier, "Provably Repairing
the ISO/IEC 9798 Standard for Entity Authentication",
Journal of Computer Security - Security and Trust
Principles, Volume 21, Issue 6, pp. 817-846, November
2013,
<https://www.cs.ox.ac.uk/people/cas.cremers/downloads/
papers/BCM2012-iso9798.pdf>.

[CapURLs] Tennison, J., Ed., "Good Practices for Capability URLs",
W3C First Public Working Draft, 18 February 2014,
<https://www.w3.org/TR/capability-urls/>.

[IANA.JWT.Claims]
IANA, "JSON Web Token (JWT)",
<https://www.iana.org/assignments/jwt>.

[IANA.MediaTypes]
IANA, "Media Types",
<https://www.iana.org/assignments/media-types>.

[IANA.OAuth.Parameters]
IANA, "OAuth Parameters",
<https://www.iana.org/assignments/oauth-parameters>.

[OpenID.Core]
Sakimura, N., Bradley, J., Jones, M.B., de Medeiros, B.,
and C. Mortimore, "OpenID Connect Core 1.0 incorporating
errata set 1", OpenID Foundation Standards, 8 November
2014,
<http://openid.net/specs/openid-connect-core-1_0.html>.

[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>.

[RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0
Threat Model and Security Considerations", RFC 6819,
DOI 10.17487/RFC6819, January 2013,
<https://www.rfc-editor.org/info/rfc6819>.

[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.

[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>.

[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>.

[RFC8725] Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
Current Practices", BCP 225, RFC 8725,
DOI 10.17487/RFC8725, February 2020,
<https://www.rfc-editor.org/info/rfc8725>.

Acknowledgements

The following people contributed to the creation of this document in
the OAuth Working Group and other IETF roles. (Affiliations at the
time of the contribution are used.)

Annabelle Backman (Amazon), Dirk Balfanz (Google), Sergey Beryozkin,
Ben Campbell (as AD), Brian Campbell (Ping Identity), Roman Danyliw
(as AD), Martin Duke (as AD), Vladimir Dzhuvinov (Connect2id), Lars
Eggert (as AD), Joel Halpern (as GENART), Benjamin Kaduk (as AD),
Stephen Kent (as SECDIR), Murray Kucherawy (as AD), Warren Kumari (as
OPSDIR), Watson Ladd (as SECDIR), Torsten Lodderstedt (yes.com), Jim
Manico, James H. Manger (Telstra), Kathleen Moriarty (as AD), Axel
Nennker (Deutsche Telecom), John Panzer (Google), Francesca Palombini
(as AD), David Recordon (Facebook), Marius Scurtescu (Google), Luke
Shepard (Facebook), Filip Skokan (Auth0), Hannes Tschofenig (ARM),
Éric Vyncke (as AD), and Robert Wilton (as AD).

The following people contributed to creating this document through
the OpenID Connect Core 1.0 [OpenID.Core].

Brian Campbell (Ping Identity), George Fletcher (AOL), Ryo Itou
(Mixi), Edmund Jay (Illumila), Breno de Medeiros (Google), Hideki
Nara (TACT), and Justin Richer (MITRE).

Authors' Addresses

Nat Sakimura
NAT.Consulting
2-22-17 Naka
Kunitachi, Tokyo 186-0004
Japan

Phone: +81-42-580-7401
Email: nat@nat.consulting
URI: https://nat.sakimura.org/

John Bradley
Yubico
Sucursal Talagante
Casilla 177
Talagante
RM
Chile

Phone: +1.202.630.5272
Email: ve7jtb@ve7jtb.com rfc9101@ve7jtb.com
URI: http://www.thread-safe.com/

Michael B. Jones
Microsoft
One Microsoft Way
Redmond, Washington 98052
United States of America

Email: mbj@microsoft.com
URI: https://self-issued.info/