Wednesday, May 19, 2010

Identity as an Attribute

A while back I posted a couple of entries on the concept of an identity token. The idea being that a client/requester/relying party could request an identity token from the Identity Provider (IdP) when authenticating the user and then use it when accessing protected resources to represent who is making the request. This becomes very important in person-to-person sharing use cases.

One such use case that recently appeared on the OpenID specs listserv is the need to access protected <Link> elements in a user's XRD/JRD. For example, I want to allow family members to be able to discover my family photo albums but keep those links restricted from public access. The basic need is that the requesting client/service needs to "prove" to my XRD provider that they are a "family member". A very easy way to do this is for the requesting client/service to obtain an "identity claim" from the family member's identity provider and pass that along to the XRD provider. This of course would most like be in the form of some structured OAuth token.

Thinking about it this way, the user's identity is really just a 3rd party asserted attribute. 3rd party because the client is the 1st party in this scenario and will be the entity presenting the attribute to other services.

This concept of 3rd party asserted attributes is not new. There have been many discussions and posts about how to obtain an "over 18" attribute from the DMV and store it in the IdP. What makes representing the user's identity different in this case is that often, the user's identity is the key that gets them access to their resources. Thus, this identity attribute has to be recognized as just a verified identifier (i.e. like relying parties want a verified email address) and not some sort of authorization token.

My one concern has to do with whether 3rd party asserted attributes should just be bearer tokens? or whether they need some holder-of-key mechanism to ensure that only the client that is issued the 3rd party asserted attribute can present it in future requests.

Previous posts:
Protecting "discovery" information?
Open Identity Token
Open Identity Token and Personal Discovery Service (Praveen Alavilli)
Continuing the discussion...

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