Friday, December 22, 2006

Identity Oracle

In a post from the summer, Bob Blakley argues that IDPs should play their cards close to the chest, never answering directly to identity requests, but instead obliquely.
Q: Where is the Joe's location?
A: He's within 300 m of your store. I'll say no more.

For Bob, doing so means that the IDP doesn't give away the bank the first time it answers an identity request from an SP, and thereby makes viable an IDP business model.

  1. I question Bob's use of 'meta' to refer to this sort of reply. While the answer 'The user is over 18' is 'data about data' and technically deserves the descriptor, 'meta' is taken in the industry, both to refer to how providers advertise their capabilities and endpoints (e.g. SAML metadata and WS-MetadataExchange for instance), and by the more nebulous identity metasystem.
  2. For dynamic data such as geolocation or presence, even were the IDP to share the actual data, the IDP remains relevant because, like the weather, wait long enough and things will change.
  3. Bob acknowledges the privacy advantages of the model but for him they are secondary to the business value.
    It was the privacy advantages (namely enabling the privacy principle of minimal disclosure) that drove the Liberty Alliance to ensure that we could support such a model. ID-Web Services Framework defines a test mechanism by which an SP can pose such questions to an IDP.
    An example of how a test would be expressed within a request.

    <TestItem objectType="profile">
    <TestOp>//Age >= ’18’</TestOp>

    the test here uses XPath.

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