[security-services] New high level SSO use cases

And I do mean high level.

I think I captured the primary one Jahan and Prateek (among others) were discussing (which is more or less what Shibboleth has,
roughly speaking).

I then included a pair of scenarios that in my mind capture most of my "fancy" requirements at a non-technical level; that is,
having the ability to pass context information (of whatever sort) from destination to source to affect the SSO process.

This would presumably be, in Bob Morgan's words, "a structured, extensible format", and is obviously ground plowed by Liberty phase
1.

Anyway, I included a few names as additional contributors on this individual submission, but please let me know if you violently
object to something and want your name taken off. ;-)

-- Scott