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

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:

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 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 has shortcomings in 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) the communication through the user agents can be monitored (containment / confidentiality failure). Due to these inherent weaknesses, several attacks against the protocol, such as Redirection URI rewriting and Mix-up attack , 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, 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 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 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. (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 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: 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 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. 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 MUST contains all the 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 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. To encrypt, JWE is used. When both signature and encryption are being applied, the JWT MUST be signed then encrypted as advised in the section 11.2 of . The result is a Nested JWT, as defined in . The Authorization Request Object MAY be sent by value as described in or by reference as described in . request and request_uri parameters MUST NOT be included in Request Objects.

The following is an 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 section 4 of OAuth 2.0. The absolute URI as defined by RFC3986 that points to the Request Object that holds authorization request parameters stated in 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 one of the following: JWS signed JWS signed and JWE encrypted 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):

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. Many WAP / feature phones do not accept large payloads. The restriction is 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 therefore the use of such is not advisable from the user experience point of view. The contents of the resource referenced by the URI MUST be a Request Object. The scheme used in the request_uri value MUST be https, as defined in 2.7.2 of RFC7230. The request_uri value MUST be reachable by the Authorization Server, and SHOULD be reachable by the Client.

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):

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 Requiest URI. The URL MUST be a HTTPS URL if it is not under the control of the Authorization Server. When it is stored under the control of the Authorization Server, it may be a URN. 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. 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):

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):

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:

The following is an example of the fetch response:

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 and the signature validation MUST be performed as defined in as well. If decryption fails, the Authorization Server MUST return an invalid_request_object error.

To perform signature validation of a JSON Web Signature signed request object, the alg Header Parameter in its 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.

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 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: 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 the use of the request_uri parameter.

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 subjectAltName dNSName identities as described in , to avoid man-in-the-middle attacks. The rules and guidelines defined in apply here, with the following considerations: Support for DNS-ID identifier type (that is, the dNSName identity in the subjectAltName extension) is REQUIRED. Certification authorities which issue server certificates MUST support the DNS-ID identifier type, and the DNS-ID identifier type MUST be present in server certificates. DNS names in server certificates MAY contain the wildcard character "*". Clients MUST NOT use CN-ID identifiers; a CN field may be present in the server certificate's subject name, but MUST NOT be used for authentication within the rules described in . SRV-ID and URI-ID as described in Section 6.5 of MUST NOT be used for comparison.

This specification requests no actions by IANA.

In addition to the all the security considerations discussed in OAuth 2.0, the security considerations in , , and needs to be considered. Also, there are several academic papers such as 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 encrypted using JWE with then considered appropriate algorithm.

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 that the symmetric key for the JWE encryption is the correct one if the JWE is using symmetric encryption. 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. 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. 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.

Although this specification does not require them, research 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 come into question in this specification are : Protected Resources (protected_resources) Authorization Endpoint (authorization_endpoint) Redirection URI (redirect_uri) Token Endpoint (token_endpoint) Further, if dynamic discovery is used, then the discovery related endpoints also come into question. In , while Redirection URI is included, others are not included in the Authorization Request. As the result, the same applies to Authorization Request Object. The lack of the link among those endpoints are sited as the cause of Cross-Phase Attacks introduced in . An extension specification should be created as a measure to address the risk.

The introdcution of redirect_uri introduces several attack possibilities.

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/jose (c) implement a time-out for obtaining the content of request_uri, and (d) do 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/json (c) implement a time-out for obtaining the content of request_uri.

Curent security considerations can be found in Recommendations for Secure Use of TLS and DTLS. This supersedes the TLS version recommendations in OAuth 2.0.

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. 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 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. In a way, it is 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 are used.) Sergey Beryozkin, Brian Campbell (Ping Identity), Vladimir Dzhuvinov (Connect2id), Michael B. Jones (Microsoft), Torsten Lodderstedt (YES) Jim Manico, Axel Nenker(Deutsche Telecom), Hannes Tschofenig (ARM), Kathleen Moriarty (as AD), and Steve Kent (as SECDIR). 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).

-14 #71 Reiterate dynamic params are included. #70 Made clear that AS must return error. #69 Inconsistency of the need to sign. Fixed Mimetype. #67 Incosistence in requiring HTTPS in request uri. #66 Dropped ISO 29100 reference. #25 Removed Encrypt only option. #59 Same with #25. -13 add TLS Security Consideration section replace RFC7525 reference with BCP195 moved front tag in FETT reference to fix XML structure changes reference from SoK to FETT -12 fixes #62 - Alexey Melnikov Discuss fixes #48 - OPSDIR Review : General - delete semicolors after list items fixes #58 - DP Comments for the Last Call fixes #57 - GENART - Remove "non-normative ... " from examples. fixes #45 - OPSDIR Review : Introduction - are attacks discovered or already opened fixes #49 - OPSDIR Review : Introduction - Inconsistent colons after initial sentence of list items. fixes #53 - OPSDIR Review : 6.2 JWS Signed Request Object - Clarify JOSE Header fixes #42 - OPSDIR Review : Introduction - readability of 'and' is confusing fixes #50 - OPSDIR Review : Section 4 Request Object - Clarify 'signed, encrypted, or signed and encrypted' fixes #39 - OPSDIR Review : Abstract - Explain/Clarify JWS and JWE fixed #50 - OPSDIR Review : Section 4 Request Object - Clarify 'signed, encrypted, or signed and encrypted' fixes #43 - OPSDIR Review : Introduction - 'properties' sounds awkward and are not exactly 'properties' fixes #56 - OPSDIR Review : 12 Acknowledgements - 'contribution is' => 'contribution are' fixes #55 - OPSDIR Review : 11.2.2 Privacy Considerations - ' It is in a way' => 'In a way, it is' fixes #54 - OPSDIR Review : 11 Privacy Considerations - 'and not specific' => 'and are not specific' fixes #51 - OPSDIR Review : Section 4 Request Object - 'It is fine' => 'It is recommended' fixes #47 - OPSDIR Review : Introduction - 'over- the- wire' => 'over-the-wire' fixes #46 - OPSDIR Review : Introduction - 'It allows' => 'The use of application security' for fixes #44 - OPSDIR Review : Introduction - 'has' => 'have' fixes #41 - OPSDIR Review : Introduction - missing 'is' before 'typically sent' fixes #38 - OPSDIR Review : Section 11 - Delete 'freely accessible' regarding ISO 29100 -11 s/bing/being/ Added history for -10 -10 #20: KM1 -- some wording that is awkward in the TLS section. #21: KM2 - the additional attacks against OAuth 2.0 should also have a pointer #22: KM3 -- Nit: in the first line of 10.4: #23: KM4 -- Mention RFC6973 in Section 11 in addition to ISO 29100 #24: SECDIR review: Section 4 -- Confusing requirements for sign+encrypt #25: SECDIR review: Section 6 -- authentication and integrity need not be provided if the requestor encrypts the token? #26: SECDIR Review: Section 10 -- why no reference for JWS algorithms? #27: SECDIR Review: Section 10.2 - how to do the agreement between client and server "a priori"? #28: SECDIR Review: Section 10.3 - Indication on "large entropy" and "short lifetime" should be indicated #29: SECDIR Review: Section 10.3 - Typo #30: SECDIR Review: Section 10.4 - typos and missing articles #31: SECDIR Review: Section 10.4 - Clearer statement on the lack of endpoint identifiers needed #32: SECDIR Review: Section 11 - ISO29100 needs to be moved to normative reference #33: SECDIR Review: Section 11 - Better English and Entropy language needed #34: Section 4: Typo #35: More Acknowledgment #36: DP - More precise qualification on Encryption needed. -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 acknowledgment. -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 take 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.