OAuth Working Group N. Sakimura
Internet-Draft Nomura Research Institute
Intended status: Standards Track J. Bradley
Expires: August 3, 2017 Ping Identity
January 30, 2017

The OAuth 2.0 Authorization Framework: JWT Secured Authorization Request (JAR)
draft-ietf-oauth-jwsreq-10

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 are 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 JWS signed and/or JWE encrypted 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.

Status of This Memo

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 http://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 August 3, 2017.

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Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

1. Introduction

The Authorization Request in OAuth 2.0 [RFC6749] utilizes query parameter serialization and 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 with confidentiality and integrity protection to be used. While TLS is used to offer communication security between the Client and the user-agent and 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 a property that

(a)
the communication through the user agents are 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); and
(c)
the communication through the user agents can be monitored (containment / confidentiality failure).

Because of these weaknesses, several attacks against the protocol, such as Redirection URI rewriting, has been discovered.

The use of application layer security mitigates these issues.

In addition, it 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, 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 that it is an RFC and so is its associated signing and encryption methods as [RFC7515] and [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. This JWT 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 the 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; and
(d)
(collection minimization) The request can be signed by a third party attesting that the authorization request is compliant with a certain policy. For example, a request can be pre-examined by a third party that all the personal data requested is strictly necessary to perform the process that the end-user asked for, and statically signed by that third party. The client would then send the request along with dynamic parameters such as state. 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 that request by reference is useful such as:

  1. When it is desirable to reduce the size of transmitted request. The use of application layer security increases the size of the request, particularly when public key cryptography is used.
  2. The client can make a signed Request Object and put it in a place that the Authorization Server can access. This may just be done by a client utility or other process, so that the private key does not have to reside on the client, simplifying programming. The downside of it is that the signed portion just become a token.
  3. When the server wants the requests to be cacheable: The request_uri may include a SHA-256 hash of the contents of the resources referenced by the Request Object URI. With this, the server knows if the resource has changed without fetching it, so it does not have to re-fetch the same content, which is a win as well. This is explained in Section 5.2.
  4. When the client does not want to do the crypto: 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", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

2. Terminology

For the purposes of this specification, the following terms and definitions in addition to what is defined in OAuth 2.0 Framework [RFC6749], JSON Web Signature [RFC7515], and JSON Web Encryption [RFC7519] apply.

2.1. Request Object

JWT [RFC7519] that holds an OAuth 2.0 authorization request as JWT Claims Set

2.2. Request Object URI

Absolute URI from which the Request Object [request_object] can be obtained

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
WAP
Wireless Application Protocol

4. Request Object

A Request Object [request_object] is used to provide authorization request parameters for an OAuth 2.0 authorization request. It contains OAuth 2.0 [RFC6749] authorization request parameters including extension parameters. The parameters are represented as the JWT claims. Parameter names and string values MUST be included as JSON strings. Since it is a JWT, JSON strings MUST be represented in UTF-8. Numerical values MUST be included as JSON numbers. It MAY include any extension parameters. This JSON [RFC7159] constitutes the JWT Claims Set defined in JWT [RFC7519]. The JWT Claims Set is then signed, encrypted, 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.

To encrypt, JWE [RFC7516] is used. Unless the algorithm used in JWE allows for the source to be authenticated, JWS signature SHOULD also be applied so that the source authentication can be done. When both signature and encryption are being applied, the JWT MUST be signed then encrypted as advised in the section 11.2 of [RFC7519]. The result is a Nested JWT, as defined in [RFC7519].

The Authorization Request Object MAY be sent by value as described in Section 5.1 or by reference as described in Section 5.2.

Required OAuth 2.0 Authorization Request parameters that are not included in the Request Object MUST be sent as query parameters. If a required parameter is missing from both the query parameters and the Request Object, the request is malformed.

request and request_uri parameters MUST NOT be included in Request Objects.

If the parameter exists in both the query string and the Authorization Request Object, the values in the Request Object take precedence. This means that if it intends to use a cached request object, it cannot include parameters such as state that are expected to differ in every request. It is fine to include them in the request object if it is going to be prepared afresh every time.

The following is a non-normative example of the Claims in a Request Object before base64url encoding and signing. Note that it includes extension variables such as "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.ew0KICJpc3MiOiAiczZCaGRSa3
  F0MyIsDQogImF1ZCI6ICJodHRwczovL3NlcnZlci5leGFtcGxlLmNvbSIsDQogInJl
  c3BvbnNlX3R5cGUiOiAiY29kZSBpZF90b2tlbiIsDQogImNsaWVudF9pZCI6ICJzNk
  JoZFJrcXQzIiwNCiAicmVkaXJlY3RfdXJpIjogImh0dHBzOi8vY2xpZW50LmV4YW1w
  bGUub3JnL2NiIiwNCiAic2NvcGUiOiAib3BlbmlkIiwNCiAic3RhdGUiOiAiYWYwaW
  Zqc2xka2oiLA0KICJub25jZSI6ICJuLTBTNl9XekEyTWoiLA0KICJtYXhfYWdlIjog
  ODY0MDAsDQogImNsYWltcyI6IA0KICB7DQogICAidXNlcmluZm8iOiANCiAgICB7DQ
  ogICAgICJnaXZlbl9uYW1lIjogeyJlc3NlbnRpYWwiOiB0cnVlfSwNCiAgICAgIm5p
  Y2tuYW1lIjogbnVsbCwNCiAgICAgImVtYWlsIjogeyJlc3NlbnRpYWwiOiB0cnVlfS
  wNCiAgICAgImVtYWlsX3ZlcmlmaWVkIjogeyJlc3NlbnRpYWwiOiB0cnVlfSwNCiAg
  ICAgInBpY3R1cmUiOiBudWxsDQogICAgfSwNCiAgICJpZF90b2tlbiI6IA0KICAgIH
  sNCiAgICAgImdlbmRlciI6IG51bGwsDQogICAgICJiaXJ0aGRhdGUiOiB7ImVzc2Vu
  dGlhbCI6IHRydWV9LA0KICAgICAiYWNyIjogeyJ2YWx1ZXMiOiBbInVybjptYWNlOm
  luY29tbW9uOmlhcDpzaWx2ZXIiXX0NCiAgICB9DQogIH0NCn0.nwwnNsk1-Zkbmnvs
  F6zTHm8CHERFMGQPhos-EJcaH4Hh-sMgk8ePrGhw_trPYs8KQxsn6R9Emo_wHwajyF
  KzuMXZFSZ3p6Mb8dkxtVyjoy2GIzvuJT_u7PkY2t8QU9hjBcHs68PkgjDVTrG1uRTx
  0GxFbuPbj96tVuj11pTnmFCUR6IEOXKYr7iGOCRB3btfJhM0_AKQUfqKnRlrRscc8K
  ol-cSLWoYE9l5QqholImzjT_cMnNIznW9E7CDyWXTsO70xnB4SkG6pXfLSjLLlxmPG
  iyon_-Te111V8uE83IlzCYIb_NMXvtTIVc1jpspnTSD7xMbpL-2QgwUsAlMGzw

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":"y9Lqv4fCp6Ei-u2-ZCKq83YvbFEk6JMs_pSj76eMkddWRuWX2aBKGHAtKlE5P
        7_vn__PCKZWePt3vGkB6ePgzAFu08NmKemwE5bQI0e6kIChtt_6KzT5OaaXDF
        I6qCLJmk51Cc4VYFaxgqevMncYrzaW_50mZ1yGSFIQzLYP8bijAHGVjdEFgZa
        ZEN9lsn_GdWLaJpHrB3ROlS50E45wxrlg9xMncVb8qDPuXZarvghLL0HzOuYR
        adBJVoWZowDNTpKpk2RklZ7QaBO7XDv3uR7s_sf2g-bAjSYxYUGsqkNA9b3xV
        W53am_UZZ3tZbFTIh557JICWKHlWj5uzeJXaw",
   "e":"AQAB"
  }

5. Authorization Request

The client constructs the authorization request URI by adding one of the following parameters but not both to the query component of the authorization endpoint URI using the application/x-www-form-urlencoded format:

request
The Request Object [request_object] that holds authorization request parameters stated in section 4 of OAuth 2.0 [RFC6749].
request_uri
The absolute URL that points to the Request Object [request_object] that holds authorization request parameters stated in the section 4 of OAuth 2.0 [RFC6749].

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?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 either

(a)
JWS signed; or
(b)
JWE encrypted (when symmetric keys are bing used); or
(c)
JWS signed and JWE encrypted.

When the Request Object is used, the OAuth 2.0 request parameter values contained in the JWS Signed and/or JWE Encrypted JWT supersede those passed using the OAuth 2.0 request syntax. Parameters MAY also be passed using the OAuth 2.0 request syntax even when a Request Object is used in the cases such as (a) to achieve backward compatibility with [RFC6749] or (b) to enable a cached, pre-signed (and possibly pre-encrypted) Request Object value to be used containing the fixed request parameters, while parameters that can vary with each request, such as state and nonce of OpenID Connect, are passed as OAuth 2.0 parameters. In such case, one needs to carefully assess the risk associated with it as unprotected parameters would create additional attack surfaces. See Section 10.2 as well.

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 a non-normative example of an Authorization Request using the request parameter (with line wraps within values for display purposes only):

  https://server.example.com/authorize?
    request=eyJhbGciOiJSUzI1NiIsImtpZCI6ImsyYmRjIn0.ew0KICJpc3MiOiA
    iczZCaGRSa3F0MyIsDQogImF1ZCI6ICJodHRwczovL3NlcnZlci5leGFtcGxlLmN
    vbSIsDQogInJlc3BvbnNlX3R5cGUiOiAiY29kZSBpZF90b2tlbiIsDQogImNsaWV
    udF9pZCI6ICJzNkJoZFJrcXQzIiwNCiAicmVkaXJlY3RfdXJpIjogImh0dHBzOi8
    vY2xpZW50LmV4YW1wbGUub3JnL2NiIiwNCiAic2NvcGUiOiAib3BlbmlkIiwNCiA
    ic3RhdGUiOiAiYWYwaWZqc2xka2oiLA0KICJub25jZSI6ICJuLTBTNl9XekEyTWo
    iLA0KICJtYXhfYWdlIjogODY0MDAsDQogImNsYWltcyI6IA0KICB7DQogICAidXN
    lcmluZm8iOiANCiAgICB7DQogICAgICJnaXZlbl9uYW1lIjogeyJlc3NlbnRpYWw
    iOiB0cnVlfSwNCiAgICAgIm5pY2tuYW1lIjogbnVsbCwNCiAgICAgImVtYWlsIjo
    geyJlc3NlbnRpYWwiOiB0cnVlfSwNCiAgICAgImVtYWlsX3ZlcmlmaWVkIjogeyJ
    lc3NlbnRpYWwiOiB0cnVlfSwNCiAgICAgInBpY3R1cmUiOiBudWxsDQogICAgfSw
    NCiAgICJpZF90b2tlbiI6IA0KICAgIHsNCiAgICAgImdlbmRlciI6IG51bGwsDQo
    gICAgICJiaXJ0aGRhdGUiOiB7ImVzc2VudGlhbCI6IHRydWV9LA0KICAgICAiYWN
    yIjogeyJ2YWx1ZXMiOiBbInVybjptYWNlOmluY29tbW9uOmlhcDpzaWx2ZXIiXX0
    NCiAgICB9DQogIH0NCn0.nwwnNsk1-ZkbmnvsF6zTHm8CHERFMGQPhos-EJcaH4H
    h-sMgk8ePrGhw_trPYs8KQxsn6R9Emo_wHwajyFKzuMXZFSZ3p6Mb8dkxtVyjoy2
    GIzvuJT_u7PkY2t8QU9hjBcHs68PkgjDVTrG1uRTx0GxFbuPbj96tVuj11pTnmFC
    UR6IEOXKYr7iGOCRB3btfJhM0_AKQUfqKnRlrRscc8Kol-cSLWoYE9l5QqholImz
    jT_cMnNIznW9E7CDyWXTsO70xnB4SkG6pXfLSjLLlxmPGiyon_-Te111V8uE83Il
    zCYIb_NMXvtTIVc1jpspnTSD7xMbpL-2QgwUsAlMGzw

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, other than that the Request Object value is retrieved from the resource at the specified URL, rather than passed by value.

When the request_uri parameter is used, the OAuth 2.0 authorization request parameter values contained in the referenced JWT supersede those passed using the OAuth 2.0 request syntax. Parameters MAY also be passed using the OAuth 2.0 request syntax even when a Request Object is used in the cases such as (a) to achieve backward compatibility with [RFC6749] or (b) to enable a cached, pre-signed (and possibly pre-encrypted) Request Object value to be used containing the fixed request parameters, while parameters that can vary with each request, such as state and nonce of OpenID Connect, are passed as OAuth 2.0 parameters. In such case, one needs to carefully assess the risk associated with it as unprotected parameters would create additional attack surfaces. See Section 10.2 as well.

Servers MAY cache the contents of the resources referenced by Request Object URIs. If the contents of the referenced resource could ever change, the URI SHOULD include the base64url encoded SHA-256 hash as defined in RFC6234 [RFC6234] of the referenced resource contents as the fragment component of the URI. If the fragment value used for a URI changes, it signals the server that any cached value for that URI with the old fragment value is no longer valid.

The entire Request URI MUST NOT exceed 512 ASCII characters. There are three reasons for this restriction.

  1. Many WAP / feature phones do not accept large payloads. The restriction is typically either 512 or 1024 ASCII characters.
  2. The maximum URL length supported by older versions of Internet Explorer is 2083 ASCII characters.
  3. On a slow connection such as 2G mobile connection, a large URL would cause the slow response and therefore the use of such is not advisable from the user experience point of view.

The contents of the resource referenced by the URL MUST be a Request Object. The scheme used in the request_uri value MUST be https, unless the target Request Object is signed in a way that is verifiable by the Authorization Server. The request_uri value MUST be reachable by the Authorization Server, and SHOULD be reachable by the Client.

The following is a non-normative 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.ew0KICJpc3MiOiAiczZCaGRSa3
  F0MyIsDQogImF1ZCI6ICJodHRwczovL3NlcnZlci5leGFtcGxlLmNvbSIsDQogInJl
  c3BvbnNlX3R5cGUiOiAiY29kZSBpZF90b2tlbiIsDQogImNsaWVudF9pZCI6ICJzNk
  JoZFJrcXQzIiwNCiAicmVkaXJlY3RfdXJpIjogImh0dHBzOi8vY2xpZW50LmV4YW1w
  bGUub3JnL2NiIiwNCiAic2NvcGUiOiAib3BlbmlkIiwNCiAic3RhdGUiOiAiYWYwaW
  Zqc2xka2oiLA0KICJub25jZSI6ICJuLTBTNl9XekEyTWoiLA0KICJtYXhfYWdlIjog
  ODY0MDAsDQogImNsYWltcyI6IA0KICB7DQogICAidXNlcmluZm8iOiANCiAgICB7DQ
  ogICAgICJnaXZlbl9uYW1lIjogeyJlc3NlbnRpYWwiOiB0cnVlfSwNCiAgICAgIm5p
  Y2tuYW1lIjogbnVsbCwNCiAgICAgImVtYWlsIjogeyJlc3NlbnRpYWwiOiB0cnVlfS
  wNCiAgICAgImVtYWlsX3ZlcmlmaWVkIjogeyJlc3NlbnRpYWwiOiB0cnVlfSwNCiAg
  ICAgInBpY3R1cmUiOiBudWxsDQogICAgfSwNCiAgICJpZF90b2tlbiI6IA0KICAgIH
  sNCiAgICAgImdlbmRlciI6IG51bGwsDQogICAgICJiaXJ0aGRhdGUiOiB7ImVzc2Vu
  dGlhbCI6IHRydWV9LA0KICAgICAiYWNyIjogeyJ2YWx1ZXMiOiBbInVybjptYWNlOm
  luY29tbW9uOmlhcDpzaWx2ZXIiXX0NCiAgICB9DQogIH0NCn0.nwwnNsk1-Zkbmnvs
  F6zTHm8CHERFMGQPhos-EJcaH4Hh-sMgk8ePrGhw_trPYs8KQxsn6R9Emo_wHwajyF
  KzuMXZFSZ3p6Mb8dkxtVyjoy2GIzvuJT_u7PkY2t8QU9hjBcHs68PkgjDVTrG1uRTx
  0GxFbuPbj96tVuj11pTnmFCUR6IEOXKYr7iGOCRB3btfJhM0_AKQUfqKnRlrRscc8K
  ol-cSLWoYE9l5QqholImzjT_cMnNIznW9E7CDyWXTsO70xnB4SkG6pXfLSjLLlxmPG
  iyon_-Te111V8uE83IlzCYIb_NMXvtTIVc1jpspnTSD7xMbpL-2QgwUsAlMGzw
  

5.2.1. URL Referencing the Request Object

The Client stores the Request Object resource either locally or remotely at a URL the Authorization Server can access. The URL MUST be HTTPS URL. This URL 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. It is RECOMMENDED that it be removed if it is known that it will not be used again or after a reasonable timeout unless access control measures are taken.

Unless the access to the request_uri over TLS provides adequate authentication of the source of the Request Object, the Request Object MUST be JWS Signed.

The following is a non-normative example of a Request Object URI value (with line wraps within values for display purposes only):

  https://client.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 a non-normative example of an Authorization Request using the request_uri parameter (with line wraps within values for display purposes only):

  https://server.example.com/authorize?
    response_type=code%20id_token
    &client_id=s6BhdRkqt3
    &request_uri=https%3A%2F%2Fclient.example.org%2Frequest.jwt
    %23GkurKxf5T0Y-mnPFCHqWOMiZi4VS138cQO_V7PZHAdM
    &state=af0ifjsldkj

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 is already cached, and parse it to recreate the Authorization Request parameters.

Note that the client SHOULD use a unique URI for each request containing distinct parameters values, or otherwise prevent the Authorization Server from caching the request_uri.

The following is a non-normative example of this fetch process:

  GET /request.jwt HTTP/1.1
  Host: client.example.org

6. Validating JWT-Based Requests

6.1. Encrypted Request Object

The Authorization Server MUST decrypt the JWT in accordance with the JSON Web Encryption [RFC7516] specification. If the result is a signed request object, signature validation MUST be performed as defined in Section 6.2 as well.

If decryption fails, the Authorization Server MUST return an invalid_request_object error.

6.2. JWS Signed Request Object

To perform JWS Signature Validation, the alg Header Parameter in the JOSE Header MUST match the value of the pre-registered algorithm. The signature MUST be validated against the appropriate key for that client_id and algorithm.

If signature validation fails, the Authorization Server MUST return an invalid_request_object error.

6.3. Request Parameter Assembly and Validation

The Authorization Server MUST assemble the set of Authorization Request parameters to be used from the Request Object value and the OAuth 2.0 Authorization Request parameters (minus the request or request_uri parameters). If the same parameter exists both in the Request Object and the OAuth Authorization Request parameters, the parameter in the Request Object is used. Using the assembled set of Authorization Request parameters, the Authorization Server then validates the request as specified in OAuth 2.0 [RFC6749].

7. Authorization Server Response

Authorization Server Response is created and sent to the client as in Section 4 of OAuth 2.0 [RFC6749] .

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.

Whenever TLS is used, the identity of the service provider encoded in the TLS server certificate MUST be verified using the procedures described in Section 6 of [RFC6125].

9. IANA Considerations

This specification requests no actions by IANA.

10. Security Considerations

In addition to the all the security considerations discussed in OAuth 2.0 [RFC6819], the security considerations in [RFC7515], [RFC7516], and [RFC7518] needs 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 request parameter, it MUST either be signed using JWS [RFC7515] or encrypted using JWE [RFC7516] with then considered appropriate algorithm.

10.2. Choice of Parameters to include in the Request Object

Unless there is a compelling reason to do otherwise, it is strongly recommended to create a request object that covers all the parameters so that the entire request is integrity protected.

This means that the request object is going to be prepared fresh each time an authorization request is made and caching cannot be used. It has a performance disadvantage, but where such disadvantage is permissible, it should be considered.

Unless the server and the client have agreed prior to the authorization request to use the non-protected parameters, the authorization server SHOULD reject a request that is not fully integrity protected and source authenticated. Note that the such agreement needs to be done in a secure fashion. For example, the developers from the server side and the client side can have a face to face meeting to come to such an agreement.

10.3. Request Source Authentication

The source of the Authorization Request MUST always be verified. There are several ways to do it in this specification.

(a)
Verifying the JWS Signature of the Request Object.
(b)
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 Request Object URI and only the Client is covered by the TLS certificate. In general, it is not a reliable method.
(c)
Authorization Server is providing an endpoint that provides a Request Object URI in exchange for a Request Object. In this case, 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. Since 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 128bit or more at the time of the writing of this specification.
(d)
A third party, such as a Trust Framework Provider, provides an endpoint that provides a Request Object URI in exchange for a Request Object. The same requirements as (b) above apply. In addition, the Authorization Server MUST know out-of-band that the Client utilizes the Trust Framework Operator.

10.4. 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. The endpoints that come into question in this specification are

(a)
Protected Resources (protected_resources);
(b)
Authorization Endpoint (authorization_endpoint);
(c)
Redirection URI (redirect_uri); and
(d)
Token Endpoint (token_endpoint).

While Redirection URI is included, others are not included in the Authorization Request Object. It is probably a good idea to include these in it to reduce the attack surface. An extension specification should be created as a preventive measure to address potential vulnerabilities that has not yet been identified.

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. ISO/IEC 29100 [ISO29100] is a freely accessible International Standard and its Privacy Principles are good to follow.

While ISO/IEC 29100 [ISO29100] is a high-level document that gives general guidance, RFC 6973 Privacy Considerations for Internet Protocols [RFC6973] gives more specific guidances on the privacy consideration for Internet Protocols. It gives excellent guidances 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 [RFC6749] and The OAuth 2.0 Authorization Framework: Bearer Token Usage [RFC6750] and not specific to this specification. In what follows, only the specific provisions 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 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.

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.

11.2. Disclosure Limitation

11.2.1. Request Disclosure

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 [RFC7516] 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 short validity period, and MUST have large enough entropy deemed necessary with applicable security policy unless the Request Object itself is JWE [RFC7516] 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.

11.2.2. Tracking using Request Object URI

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 per-user Request Object URI is used. A third party may observe it through browser history etc. and start correlating the user's activity using it. It is in a way a data disclosure as well and should be avoided.

Therefore, per-user Request Object URI should be avoided.

12. Acknowledgements

The following people contributed to the creation of this document in the OAuth WG. (Affiliations at the time of the contribution is used.)

Sergey Beryozkin, Brian Campbell (Ping Identity), Vladimir Dzhuvinov (Connect2id), Michael B. Jones (Microsoft), Torsten Lodderstedt (Deutsche Telecom) Jim Manico, Axel Nenker(Deutsche Telecom), Hannes Tschofenig (ARM), Denis Pinkas, Kathleen Moriarty (as AD), and Steve Kent (as SECDIR).

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), Michael B. Jones (Microsoft), Breno de Medeiros (Google), Hideki Nara (TACT), Justin Richer (MITRE).

In addition, the following people contributed to this and previous versions through the OAuth Working Group.

Dirk Balfanz (Google), James H. Manger (Telstra), John Panzer (Google), David Recordon (Facebook), Marius Scurtescu (Google), Luke Shepard (Facebook).

13. Revision History

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14. References

14.1. Normative References

, "
[ISO29100]ISO/IEC 29100 Information technology - Security techniques - Privacy framework", December 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[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.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI 10.17487/RFC6234, May 2011.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, October 2012.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization Framework: Bearer Token Usage", RFC 6750, DOI 10.17487/RFC6750, October 2012.
[RFC6819] Lodderstedt, T., McGloin, M. and P. Hunt, "OAuth 2.0 Threat Model and Security Considerations", RFC 6819, DOI 10.17487/RFC6819, January 2013.
[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.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014.
[RFC7515] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", RFC 7516, DOI 10.17487/RFC7516, May 2015.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, May 2015.
[RFC7519] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015.
[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.

14.2. 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, Pages 817-846, November 2013.
[OpenID.Core] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B. and C. Mortimore, "OpenID Connect Core 1.0", OpenID Foundation Standards, February 2014.

Authors' Addresses

Nat Sakimura Nomura Research Institute 1-6-5 Marunouchi, Marunouchi Kitaguchi Bldg. Chiyoda-ku, Tokyo 100-0005 Japan Phone: +81-3-5533-2111 EMail: n-sakimura@nri.co.jp URI: http://nat.sakimura.org/
John Bradley Ping Identity Casilla 177, Sucursal Talagante Talagante, RM Chile Phone: +44 20 8133 3718 EMail: ve7jtb@ve7jtb.com URI: http://www.thread-safe.com/