I am keen for the RP to identify itself when it performs discovery – and I would love this feature to be in 2.0 before it is finalized.
The proposal is very simple (to describe and to implement): RPs add a “From:” HTTP header field to HTTP requests made during the discovery phase. The underlying premise is that a user has many varied user<->RP relationships, and it is easiest if the same OpenID URL can be used to access them all. The issue is how to support the varied relationships. Some OPs will support some variations, but no OP can support all possible variations (many are user-specific). Identifying the RP during discovery enhances the ability to choose the appropriate OP for a specific user<->RP relationship. The need for this feature can be seen in the PAPE draft (§3 Advertising Supported Policies) and OpenID 2.0 draft (§12 Extensions). They support different OPs when authenticating to different RPs - but with very limited options, and with the RP in control of the choice. The user (via the server hosting their OpenID URL) should also be in control. http://openid.net/specs/openid-provider-authentication-policy-extension-1_0-02.html#advertising http://openid.net/specs/openid-authentication-2_0-12.html#extensions Both specify how a Yadis document can list multiple OPs, each associated with different OpenID protocol versions, understanding different OpenID extensions, and supporting different authentication policies. These details “aide in the process of a RP selecting which OP they wish to interact with”. The appropriate OP can only be chosen **by the RP** based on a very limited set of pre-defined <xrd:Type> URIs. When that works… great. When it doesn’t, the site hosting the OpenID URL should be able to choose the appropriate OP based on the RP’s identity. For that it needs the RP identity during discovery, hence the “From:” HTTP request header. Previously mentioned use cases: Alice wants to use a single OpenID URL and -- 1. She wants to use different OPs when logging in to different RPs. 2. An OP is not accessible to particular RPs (eg an internal company OP is not accessible by RPs on the Internet). 3. Different RPs whitelist different (non-overlapping) sets of OPs. 4. A particular RP requires PAPE support, which only Alice’s non-preferred OP supports. ________________________________________ From: Manger, James H Sent: Wednesday, 17 October 2007 12:59 PM To: 'specs@openid.net' Subject: [OpenID] identify RP when it gets OpenID URL It can be useful to know who the Relying Party (RP) is during the discovery phase. That is, the RP should state their identify when they are looking up a user’s OpenID URL (Claimed Identifier). Use case: Alice wants to use different OPs for different RPs, while keeping the same URL (eg http://alice.example.net/). For instance, when logging into a service hosting her backups she wants to use an OP that requires a one-time password from a hardware token for each access. However, when leaving comments on blogs Alice wants to authenticate using an OP that only requires a password and uses a persistent cookie so she only has to log in once a day. Problem: Only one OP can be specified with a <link rel="openid2.provider"…/> element or in a Yadis document. [A Yadis document may be able to list many OPs, but I don’t think there is any mechanism for the RP to pick the right one.] Solution: The RP could include a From HTTP header when performing discovery. Instead of serving a static HTML page (or Yadis document) at http://alice.example.net/, the page could be dynamically generated based on the value of the From header. Suggested text for the authentication spec (draft 12): Add the following paragraph at the end of section 7.3 Discovery: “The Relying Party MUST include a From HTTP header field in each HTTP request made during discovery. The From field holds an email address for the RP (eg From: [EMAIL PROTECTED]) [RFC2616]. This enables the discovered information to vary based on the RP. The From field is not authenticated so it is not appropriate to use for access control.” Other solutions: The source IP address of the discovery request will often identify the RP, but this would be an unreliable mechanism due to proxies, clusters, load balancing, and changes at the RP. Separate user-supplied identifiers could be used, but that unnecessarily complicates the system for users. OPs can offer different authentication mechanisms based on the openid.return_to or openid.realm parameter in an authentication request. However, the user has less flexibility when they have to relying on OPs. _______________________________________________ specs mailing list specs@openid.net http://openid.net/mailman/listinfo/specs
