OpenID is not a provisioning engine
In talking about the future possibilities of OpenID 2.0 and the Attribute Exchange extension, James Henstridge mentions,
Imagine being able to update your shipping address in one place when you move house and having all the online retailers you use receive the updated address immediately. Or changing your email address and having all the bugzilla instances you use pick up the new address instantly (perhaps requiring you to verify the new address first, of course).
While I agree this kind of experience would be very neat, it is not a use case for OpenID nor the Attribute Exchange extension.
I am not surprised to hear someone say this, as this is a common point of confusion here at USC in regards to Shibboleth. When it comes to attribute delivery, both OpenID and SAML are primarily designed to provide data at the time of login 1. So this means that if a user never logs in to your service, you never get any data about them. And if a user’s data changes since their last login, you don’t find out about until they next login, since that is the only time attribute delivery occurs. It is also important to note that you are typically only getting data about the user that is logging in, no one else. You can’t treat an OpenID provider as a lookup service to get data about some other user.
So how does a relying party update their data without waiting on the user to login again? One option is to have the data pushed to each service using some kind of messaging hub. There is a whole market for enterprise messaging complete with its own set of acronyms like ESB, EMS, EAI, and many many more. I’m particularly interested in a project developed by a colleague of mine in Sweden called JEvent, which uses the XMPP Publish-Subscribe protocol to deliver these types of messages using a standard XMPP server in the middle. Your Jabber messaging window becomes your console. :)
The other method of getting at user data is for each relying party to pull the data. This is the model we use at USC, where that mechanism for pulling data is LDAP. A number of services on campus use LDAP to address both use cases mentioned above – refreshing data about users, as well as looking up data about someone other than the user who logged in. So what’s the equivalent in the decentralized OpenID world? Well honestly there isn’t anything just yet but we have a good foundation. Thanks to microformats like hCard, you can publish your data in a standard, machine-parsable format that your online retailers or bugzilla instances could watch periodically. When you update your hCard on your homepage they can respond in kind, perhaps by immediately updating their databases or sending you a confirmation email of the change. Right now all of this data is decentralized, published on personal blogs and webpages. I don’t argue that this data should certainly be under individual control, but it puts an awful large burden on the individual service providers to do all that spidering. I don’t know what the answer is, but I’ve been thinking about an hCard crawler with an LDAP front-end as a simple place to start. Configure Apple AddressBook or Outlook to use LDAP, and you’re off and running.
SAML is actually a little more flexible here, but it’s not the common use case ↩︎
Comments and responses
The OpenID attribute exchange protocol does define a method for an OP to push changes out to RPs, so provided that part of the protocol is implemented the RP does not have to wait for the user to re-authenticate.
While you might not be able to rely on this in the wild right now, you can in more controlled systems (e.g. using OpenID as a single sign-on system for a group of web sites).
For many years Semantic Web technologies have been weak on (distributed) authentication and the like, so it's quite funny to see the question "So what's the equivalent [of LDAP] in the decentralized OpenID world?".
The decentralised OpenID world is the Web, and the Web of Data story is pretty well figured out with RDF (check the material around Linked Data). Specifically for the LDAP kind of situation, you'd probably want FOAF + vCard/RDF terms.
Microformats like hCard are consistent with this, and can be directly interpreted as RDF using GRDDL.
(I forgot to mention there's now a foaf:openid property)