It’s the same url that you get redirected to if you follow the “main link” for U-Prove off of MSCOM at the moment:
However, it failed to load with what amounts to a permissions error:
Notice in the above that I’m signed in, though.
If I sign out, then the link works fine:
Perhaps my Connect account has been tagged with some kind of “he’s eeeeevil!” bit, but it’s certainly the first time I’ve had more permission on a site being anonymous than logged in 🙂