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

The Authorization Request in OAuth 2.0 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:

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 has a property that the communication through the user agents are not integrity protected and thus the parameters can be tainted (integrity protection failure); the source of the communication is not authenticated (source authentication failure); and 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 encoding has been chosen because of its close relationship with JSON, which is used as OAuth's response format; its developer friendliness due to its textual nature; its relative compactness compared to XML; its development status that it is an RFC and so is its associated signing and encryption methods as and ; 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 flows. The request parameter is a JSON Web Token (JWT) 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 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: (integrity protection) The request can be signed so that the integrity of the request can be checked ; (source authentication) The request can be signed so that the signer can be authenticated ; (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 (collection minimization) The request can be signed by a third party attesting that the authorization request is compliant to 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 are useful such as: 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. The client can make a signed Request Object and put it at 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. Downside of it is that the signed portion just become a token. 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 . 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 .

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.

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.

JWT that holds an OAuth 2.0 authorization request as JWT Claims Set

Absolute URI from which the Request Object can be obtained

The following abbreviations are common to this specification. Javascript Object Notation JSON Web Token JSON Web Signature JSON Web Encryption Uniform Resource Identifier Uniform Resource Locator Wireless Application Protocol

A Request Object is used to provide authorization request parameters for an OAuth 2.0 authorization request. It contains OAuth 2.0 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 constitutes the JWT Claims Set. The JWS Claims Set is then signed, encrypted, 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. To encrypt, JWE is used. Unless the algorithm used in JWE allows for the source to be authenticated, JWS signature should also be applied. In this case, it MUST be signed then encrypted, with the result being a Nested JWT, as defined in JWT. The Authorization Request Object may be sent by value as described in or by reference as described in . 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".

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

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):

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: The Request Object that holds authorization request parameters stated in the section 4 of OAuth 2.0. The absolute URL that points to the Request Object that holds authorization request parameters stated in the section 4 of OAuth 2.0. 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:

The value for the request parameter is abbreviated for brevity. The authorization request object MUST be either JWS signed; or JWE encrypted; or 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 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 as well.

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):

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 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 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. Many WAP / feature phones do not accept large payloads. The restriction are typically either 512 or 1024 ASCII characters. The maximum URL length supported by older versions of Internet Explorer is 2083 ASCII characters. On a slow connection such as 2G mobile connection, a large URL would cause the slow response and using 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):

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 is 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):

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):

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:

The Authorization Server MUST decrypt the JWT in accordance with the JSON Web Encryption specification. If the result is a signed request object, signature validation MUST be performed as defined in as well. If decryption fails, the Authorization Server MUST return invalid_request_object error.

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 invalid_request_object error.

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.

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: The request_uri in the Authorization Request returns an error or contains invalid data. The request parameter contains an invalid Request Object. The Authorization Server does not support the use of the request parameter. The Authorization Server does not support use of the request_uri parameter.

Client implementations supporting the Request Object URI method MUST support TLS as recommended in 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 ciphersuite 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 .

This specification requests no actions by IANA.

In addition to the all the security considerations discussed in OAuth 2.0, the following security considerations should be taken into account.

When sending the authorization request object through request parameter, it MUST either be JWS signed with then considered appropriate algorithm or encrypted using .

Unless there is a compelling reasons 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.

The source of the Authorization Request MUST always be verified. There are several ways to do it in this specification. Verifying the JWS Signature of the Request Object. 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. 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. 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 applies. In addition, the Authorization Server MUST know out-of-band that the Client utilizes the Trust Framework Operator.

Although this specification does not require them, researchs such as 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 comes into question in this specification are Protected Resources (protected_resources); Authorization Endpoint (authorization_endpoint); Redirection URI (redirect_uri); and 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.

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 is a freely accessible International Standard and its Privacy Principles are good to follow. Most of the provision would apply to The OAuth 2.0 Authorization Framework and The OAuth 2.0 Authorization Framework: Bearer Token Usage and 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. 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 Auhtorization 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 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 of one-time use and MUST have large enough entropy deemed necessary with applicable security policy unless the Request Object itself is JWE Encrypted.

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.

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 (Deutche Telecom) Jim Manico, Axel Nenker(Deutche Telecom), Hannes Tschofenig (ARM). 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), 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).

-09 Minor Editorial Nits. Section 10.4 added. Explicit reference to Security consideration (10.2) added in section 5 and section 5.2. , (add yourself) removed from the acknowledgement. -08 Applied changes proposed by Hannes on 2016-06-29 on IETF OAuth list recorded as https://bitbucket.org/Nat/oauth-jwsreq/issues/12/. TLS requirements added. Security Consideration reinforced. Privacy Consideration added. Introduction improved. -07 Changed the abbrev to OAuth JAR from oauth-jar. Clarified sig and enc methods. Better English. Removed claims from one of the example. Re-worded the URI construction. Changed the example to use request instead of request_uri. Clarified that Request Object parameters takes precedence regardless of request or request_uri parameters were used. Generalized the language in 4.2.1 to convey the intent more clearly. Changed "Server" to "Authorization Server" as a clarification. Stopped talking about request_object_signing_alg. IANA considerations now reflect the current status. Added Brian Campbell to the contributors list. Made the lists alphabetic order based on the last names. Clarified that the affiliation is at the time of the contribution. Added "older versions of " to the reference to IE uri length limitations. Stopped talking about signed or unsigned JWS etc. 1.Introduction improved. -06 Added explanation on the 512 chars URL restriction. Updated Acknowledgements. -05 More alignment with OpenID Connect. -04 Fixed typos in examples. (request_url -> request_uri, cliend_id -> client_id) Aligned the error messages with the OAuth IANA registry. Added another rationale for having request object. -03 Fixed the non-normative description about the advantage of static signature. Changed the requirement for the parameter values in the request itself and the request object from 'MUST MATCH" to 'Req Obj takes precedence. -02 Now that they are RFCs, replaced JWS, JWE, etc. with RFC numbers. -01 Copy Edits.