| OAuth Working Group | N. Sakimura |
| Internet-Draft | NAT.Consulting |
| Intended status: Standards Track | J. Bradley |
| Expires: February 21, 2021 | Yubico |
| M. Jones | |
| Microsoft | |
| August 20, 2020 |
The OAuth 2.0 Authorization Framework: JWT Secured Authorization Request (JAR)
draft-ietf-oauth-jwsreq-28
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, and (b) the source of the communication is not authenticated. 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 property of the Authorization Request is attained. The request can be sent by value or by reference.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 21, 2021.
Copyright (c) 2020 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.
The Authorization Request in OAuth 2.0 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 as well as the user-agent and the Authorization Server, TLS sessions are terminated in the user-agent. In addition, TLS sessions may be terminated prematurely at some middlebox (such as a load balancer).
As the result, the Authorization Request of [RFC6749] has shortcomings in that:
Due to these inherent weaknesses, several attacks against the protocol, such as Redirection URI rewriting and Mix-up attack [FETT], 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 third party so that a client application cannot request more permissions than previously agreed. This offers an additional degree of privacy protection.
Furthermore, passing the request by reference allows the reduction of over-the-wire overhead.
The JWT encoding has been chosen because of
The parameters request and request_uri are introduced as additional authorization request parameters for the OAuth 2.0 flows. The request parameter is a JSON Web Token (JWT) 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 can be passed to the authorization endpoint by reference, in which case the parameter request_uri is used instead of the request.
Using JWT as the request encoding instead of query parameters has several advantages:
There are a few cases that request by reference is useful such as:
This capability is in use by OpenID Connect [OpenID.Core].
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.
For the purposes of this specification, the following terms and definitions in addition to what is defined in OAuth 2.0 Framework, JSON Web Signature, and JSON Web Encryption apply.
JSON Web Token (JWT) whose JWT Claims Set holds the JSON encoded OAuth 2.0 authorization request parameters.
Absolute URI that references the set of parameters comprising an OAuth 2.0 authorization request. The contents of the resource referenced by the URI are a Request Object, 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 the Authorization Server. The former 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 and 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.
The following abbreviations are common to this specification.
A Request Object 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 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. It MAY include any extension parameters. This JSON object constitutes the JWT Claims Set defined in JWT. The JWT Claims Set is then signed or signed and encrypted.
To sign, JSON Web Signature (JWS) is used. The result is a JWS signed JWT. 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 specification. The value of aud should be the value of the Authorization Server (AS) issuer as defined in RFC8414.
To encrypt, JWE 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 has the mime-type 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 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 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 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"
}
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:
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.
For example, the client directs the end user's 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:
The client MAY send the parameters included in the request object duplicated in the query parameters as well for the backward compatibility etc. However, the authorization server supporting this specification MUST only use the parameters included in the request object.
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
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, other than that the Request Object value is retrieved from the resource identified by the specified URI rather than passed by value.
The entire Request URI MUST NOT exceed 512 ASCII characters. There are three reasons for this restriction.
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):
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 Client stores the Request Object resource either locally or remotely at a URI the Authorization Server can access. Such facility may be provided by the authorization server or a 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 5.1.4.2.2 of [RFC6819] and Good Practices for Capability URLs. It is RECOMMENDED that it 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 third-party Trust Framework Provider (TFP) hosts the Request Object.
https://tfp.example.org/request.jwt/
GkurKxf5T0Y-mnPFCHqWOMiZi4VS138cQO_V7PZHAdM
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
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 is stored in a way so that it can retrieve it through other mechanism securely, and parse it to recreate the Authorization Request parameters.
The following is an example of this fetch process. In this example, a third-party Trust Framework Provider (TFP) 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 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
If the request object is encrypted, the Authorization Server MUST decrypt the JWT in accordance with the JSON Web Encryption specification.
The result is a signed request object.
If decryption fails, the Authorization Server MUST return an invalid_request_object error.
The Authorization Server MUST validate the signature of the JSON Web Signature signed Request Object. The signature MUST be validated using the key for that client_id and the algorithm specified in the alg Header Parameter.
If signature validation fails, the Authorization Server MUST return an invalid_request_object error.
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.
If the validation fails, then the Authorization Server MUST return an error as specified in OAuth 2.0.
Authorization Server Response is created and sent to the client as in Section 4 of OAuth 2.0.
In addition, this document uses these additional error values:
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).
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:
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 need to be 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].
This specification adds the following values to the "OAuth Authorization Server Metadata" registry [IANA.OAuth.Parameters] established by [RFC8414].
This specification adds the following values to the "OAuth Dynamic Client Registration Metadata" registry [IANA.OAuth.Parameters] established by [RFC7591].
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], which can be used to indicate that the content is a JWT containing Request Object claims.
In addition to the all the security considerations discussed in OAuth 2.0, 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.
When sending the authorization request object through request parameter, it MUST either be signed using JWS or signed then encrypted using JWS and JWE respectively, with then considered appropriate algorithms.
The source of the Authorization Request MUST always be verified. There are several ways to do it:
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. The following endpoints defined in [RFC6749], [RFC6750], and [RFC8414] are RECOMMENDED by this specification to use this practice :
Further, if dynamic discovery is used, then this practice also applies to the discovery related endpoints.
In [RFC6749], while Redirection URI is included in the Authorization Request, others are not. As a result, the same applies to Authorization Request Object.
The lack of linkage among those endpoints is cited as the cause of the Cross-Phase Attacks described in [FETT]. An extension specification could be created providing this linkage as a means to address the risks.
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.
A set of malicious client can launch a DoS attack to the authorization server by pointing the request_uri to a URI that returns extremely large content or extremely slow to respond. Under such an attack, the server may use up its resource and start failing.
Similarly, a malicious client can specify the request_uri value that itself points to an authorization request URI that uses request_uri to cause the recursive lookup.
To prevent such attack to succeed, the server should (a) check that the value of request_uri parameter does not point to an unexpected location, (b) check the content type of the response is application/oauth.authz.req+jwt, (c) implement a time-out for obtaining the content of request_uri, and (d) not perform recursive GET on the request_uri.
The value of request_uri is not signed thus it can be tampered by Man-in-the-browser attacker. Several attack possibilities rise because of this, e.g., (a) attacker may create another file that the rewritten URI points to making it possible to request extra scope (b) attacker launches a DoS attack to a victim site by setting the value of request_uri to be that of the victim.
To prevent such attack to succeed, the server should (a) check that the value of request_uri parameter does not point to an unexpected location, (b) check the content type of the response is application/oauth.authz.req+jwt, and (c) implement a time-out for obtaining the content of request_uri.
Unless the protocol used by client and the server is locked down to use OAuth JAR, it is possible for an attacker to use RFC6749 requests to bypass all the protection provided by this specification.
To prevent it, this specification defines a new client metadata and server metadata require_signed_request_object whose value is a boolean.
When the value of it as a 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". If omitted, the default value is false.
When the value of it as a 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". If omitted, the default value is false.
Current security considerations can be found in Recommendations for Secure Use of TLS and DTLS. This supersedes the TLS version recommendations in OAuth 2.0.
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.
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 Requests 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.
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. RFC 6973 Privacy Considerations for Internet Protocols gives excellent guidance on the enhancement of protocol design and implementation. The provision listed in it should be followed.
Most of the provision would apply to The OAuth 2.0 Authorization Framework and The OAuth 2.0 Authorization Framework: Bearer Token Usage and are not specific to this specification. In what follows, only the specific provisions to this specification are noted.
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 Trust Framework Provider can help the user by examining the Client request and comparing to the proposed processing by the Client and certifying the request. After the certification, the Client, when making an Authorization Request, can submit Authorization Request to the Trust Framework Provider to obtain the Request Object URI. This process is two steps:
Upon receiving such 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 Trust Framework Provider. Then, the Authorization Server issues HTTP GET request to the Request Object URI. Upon connecting, the Authorization Server MUST verify 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 Trust Framework Operator for the adherence to the Collection Limitation principle.
This specification allows extension parameters. These may include potentially sensitive information. Since URI query parameter 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 JWE encrypt the request object.
Where 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, have a short validity period, and MUST have large enough entropy deemed necessary with applicable security policy unless the Request Object itself is JWE Encrypted. 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 128bit or more at the time of the writing of this specification.
Even if the protected resource does not include a 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.
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), Sergey Beryozkin, Ben Campbell (as AD), Brian Campbell (Ping Identity), Roman Danyliw (as AD), Vladimir Dzhuvinov (Connect2id), Joel Halpern (as GENART), Benjamin Kaduk (as AD), Stephen Kent (as SECDIR), Murray Kucherawy (as AD), Warren Kumari (as OPSDIR), Torsten Lodderstedt (yes.com), Jim Manico, Axel Nennker (Deutsche Telecom), Hannes Tschofenig (ARM), Dirk Balfanz (Google), James H. Manger (Telstra), Kathleen Moriarty (as AD), John Panzer (Google), David Recordon (Facebook), Marius Scurtescu (Google), Luke Shepard (Facebook), Filip Skokan (Auth0), Éric Vyncke (as AD), and Robert Wilton (as AD).
The following people contributed to creating this document through the OpenID Connect Core 1.0.
Brian Campbell (Ping Identity), George Fletcher (AOL), Ryo Itou (Mixi), Edmund Jay (Illumila), Breno de Medeiros (Google), Hideki Nara (TACT), Justin Richer (MITRE).
Note to the RFC Editor: Please remove this section from the final RFC.
-28
-27
-20
-19
-17
-16
-15
-14
-13
-12
-11
-10
-09
-08
-07
-06
-05
-04
-03
-02
-01