Internet DRAFT - draft-bradley-jwt-encoded-oauth-state
draft-bradley-jwt-encoded-oauth-state
Network Working Group J. Bradley, Ed.
Internet-Draft Ping
Intended status: Experimental May 04, 2014
Expires: November 5, 2014
Encoding claims in the OAuth 2 state paramater using a JWT
draft-bradley-jwt-encoded-oauth-state-00
Abstract
This draft provides a method for a client to encode one or more
elements encoding information about the session into the OAuth 2
"state" paramater.
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].
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
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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 November 5, 2014.
Copyright Notice
Copyright (c) 2014 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
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to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. The state JSON Web Token claims . . . . . . . . . . . . . . . 3
3. Validating the state paramater . . . . . . . . . . . . . . . 4
4. Creating a xsrf claim value. . . . . . . . . . . . . . . . . 4
4.1. Statefull Clients. . . . . . . . . . . . . . . . . . . . 4
4.2. Stateless Clients. . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
In the OAuth 2.0 Authorization protocol [RFC6749] , the Authorization
server SHOULD perform an exact string comparison of the
"redirect_uri" paramater with the "redirect_uri" paramater registered
by by the client. This is essential for stopping token leakage to
third parties in the OAuth implicit flow.
As a result of this clients can not safely add extra query paramaters
to the "redirect_uri" paramater that encode additional client state
information.
The Client MUST use the "state" paramater to encode both Cross Site
Request Forgery protection and any other state information it wishes
to preserve for itself regarding the authorization request.
This draft proposes a mechanism whereby multiple state attributes can
be encoded into a JSON Web Token [JWT] for use as the value of the
"state" paramater.
The JWT may be sent without integrity protection, with integrity
protection [JWA], or with both integrity and confidentiality
protection [JWE]. The client is free to choose the appropriate
protection for it's use-case as the "state" paramater is treated as
opaque by the Authorization Server (AS).
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2. The state JSON Web Token claims
The OAuth Authorization request "state" paramater consists of a
[JWT], optionally signed with [JWS] or encrypted with [JWE], whose
payload contains claims as defined here.
xsrf REQUIRED. string containing a verifiable identifier for the
browser session, that cannot be guessed by a third party. The
verification of this element by the client protects it from
accepting authorization responses generated in response to
requests generated by third parities.
kid RECOMMENDED if signed. Identifier of the key used to sign this
client identifier at the issuer.
iat OPTIONAL. Timestamp of when this Authorization Request was
issued.
iss OPTIONAL. string identifying the party that issued this state
value.
aud OPTIONAL. string identifying the client that this state value is
intended for.
target_uri OPTIONAL. URI containing the location the user agent is
to be redirected to after authorization.
as OPTIONAL. string identifying the authorization server that this
request was sent to.
The issuer may add additional claims to the token. The producer and
the consumer of the JWT are the same or closely related entities so
collision resistance of claim names should not be a concern.
The issuer SHOULD sign the JWT with JWS [JWS] in such a way that it
can verify the signature. The JWA [JWA] algorithm HS256 with a key
of 256bits is recommended.
The issuer MAY sign the JWT with JWA algorithm none if integrity
protecting the contents of the "state" paramater is not required.
If the "state" paramater contains information the client dosen't want
to disclose to the Authorization server or user, the issuer MAY
encrypt the JWT with JWE. The JWA [JWA] algorithm ("alg") of "dir"
and encryption algorithm ("enc") of "A128CBC-HS256" are recommended
for symmetric encryption.
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3. Validating the state paramater
Upon receiving a state paramater the client must validate its
integrity. The client parses it as a JWT. It then verifies the
signature if the JWT (if signed) using JWS [JWS]. T he key used to
sign the JWT MAY be indicated by the kid field. The client MAY use
other means to validate the JWT and determine its authenticity.
The client then reads the fields inside the JWT and uses these to
configure the user experience and security parameters of the
authorization.
The "xsrf" claim MUST be validated by the client by comparing it to
the secret information that it used to create the "xrsf" value.
4. Creating a xsrf claim value.
The client MUST create a value that cannot be guessed by a third
party attacker and used to forge requests. There are many possible
ways to create this value. For reference two common ways will be
listed.
It is completely up to the purview of the particular client which
generation methods, and which claims, they will accept.
4.1. Statefull Clients.
Many clients that are web servers maintain session state for browsers
in a server side store.
These clients can generate a random value with sufficient entropy
that an attacker cannot guess future values. This value can be
stored in the server side store and used directly as the value of
"xsrf".
4.2. Stateless Clients.
Some clients that are web servers maintain session state for browsers
using browser stored cookies or HTML5 local storage.
These clients can generate a hash value based on a HTTPS: bound
session cookie or other browser side information that is not
accessible to third parties. This hash value can directly as the
value of "xsrf".
While OAuth strongly recommends that clients use TLS to secure there
endpoints, if a client is not using TLS it MUST produce the value of
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"xsrf" by using a HMAC algorithm with a secret known only to itself
over the browser stored information.
5. IANA Considerations
[ maybe we register the "xsrf" claim above? ]
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
Some information in the state JWT such as target uri for redirecting
the user to might have some security impact is the user modifies them
intentionally or unintentionally. To prevent tampering with the
"state" value the client may integrity protect the contents of the
JWT.
The client may have information that it wants to protect from
disclosure to the Authorization server, in loggs. to proxies, or to
the user. In this case encrypting the JWT as a JWE is required to
protect the confidentiality of the state information.
7. Acknowledgements
8. Normative References
[JWA] Jones, M., "JSON Web Algorithms (JWA)", draft-ietf-jose-
json-web-algorithms (work in progress), April 2014.
[JWE] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
draft-ietf-jose-json-web-encryption (work in progress),
April 2014.
[JWS] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", draft-ietf-jose-json-web-signature (work
in progress), April 2014.
[JWT] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", draft-ietf-oauth-json-web-token (work in
progress), March 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
6749, October 2012.
Author's Address
John Bradley (editor)
Ping Identity
Email: ve7jtb@ve7jtb.com
URI: http://www.thread-safe.com/
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