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$Revision: 1.7 $ of $Date: 2006/03/17 23:16:07 $
At the W3C security workshop this week, I finally got to study SXIP in some detail after hearing about it and wondering how it compares to OpenID, Yadis, and the other "Identity 2.0" techniques brewing. And just in time, with a DIX/SXIP BOF at the Dallas IETF next week.
There was so much to soak in at the workshp that I didn't manage to talk much with John Merrells in the breaks, and the slides[@@linkme] flew by pretty quickly in his short 20 minute timeslot, but I get the impression that SXIP has the essential architectural features that got me excited about OpenID:
single sign-on for people (personas)
relying parties can delegate password management
The three-party topology is similar to Kerberos (and parts of HTTP digest authentication that have probably never been deployed); the interesting thing about these technologies is the way they integrate with the deployed and emerging Web.
Both OpenID and DIX/SXIP use typed links to connect persona pages to authentication services. In OpenID, it looks like:
... but loses points for squatting in URI space. dix: is unregistered, and to register it would be a poor use of scarce community resources (URI scheme names). Besides, we want to be able to look up homesite in the Web. Available representations are good for the Web.
Also, values of the rel attribute aren't URIs; the way to ground them in URI space is to use the profile attribute. So my suggestion is to use:
One of the benefits of using http URIs to ground the terms is that we can then mix with all the existing HTTP-based goodies like GRDDL (see TAG issue RDFinXHTML-35). With a suitable namespace document and XSLT transformation, a persona page with the above markup looks like this to Semantic Web agents:
This gets particularly interesting when you move up the stack from DIX to the other parts of SXIP, i.e. the data/claims exchange. SXIP defines a bunch of properties for name, email address, etc. I hope to study the overlap with P3P, FOAF, hCard/vCard, XFN, and the like. Let's see... how many of these look familiar?
property./sxip.net/birthDate/birthYear=Year of Birth
property./sxip.net/birthDate/birthMonth=Month of Birth
property./sxip.net/birthDate/birthDay=Day of Birth
Microsoft InfoCard, another technology presented at the workshop, has some of the same architectural features. It uses Web Services Endpoint References where DIX and OpenID use plain old URIs. Boo! (see TAG issue endPointRefs-47). It uses ws-trust at some level; I'm not sure whether ws-trust is use just at the DIX/OpenID level or whether it also includes claims exchange. I'm also not quite clear how the Liberty/SAML stack relates. There was a little discussion of that at the workshop, but not much.
A couple examples show a big overlap in the relevant claims/properties:
Phil Archer of ICRA presented the RDF-based work that's now a W3C XG; his main use case is safe browsing for children, but he discussed the applicability to "mobileOK" labels, and somebody asked a question about using these labels to connect digital signature cerficate authorities. Aha! Exactly! I showed him TimBL's Semantic Web Trust approach. I hope we get to follow up on that.
Philosophy, Terminology, and WikiConsensus
Some of the technical presentations evoked criticism about confusing terminology. On the one hand, "what is identity?" looks like a philosophical problem that no self-respecting engineer should touch with a 10-foot pole, but on the other hand, wording and consistency seems to have an important impact on usability. I had a number of criticism about 'puns' in my Jun 2005 review of OpenID. And there's the issue of specialist terminology like relying party vs words that grandma understands.
This looks like a pattern language, to me; i.e. just the sort of thing that WikiWikiWeb is good for.
The Identity Gang Lexicon seems to be a pattern language developed in a wiki, but it doesn't seem to be open to all comers, so it only represents the consensus of that group. I have noodled on using wikipedia for TAG work on terminology.