Whobar is a cool library from Sxip that simplies the integration of some of the various identity systems into sites.
This pic shows Whobar in action at Sxore.
I guess the user would see the same interface at any other site that implemented Whobar.
Note: the use of 'Homesite' on the left, while perhaps appropriate for Sxore, seems to tie it too closely to Sxip for the general case? I wonder if this is configurable?
The above pic hilites the usability challenge of how to present log-in and/or registration options to a user. I'm no UI designer but have to question whether the above is optimal. As the number of options for logging-in grows, and the opportunity for confused users grows accordingly, maybe we need to separate out the possibility of registration, rather than intermixing the two as the above does?
Whatever does turn out to be the best (in the sense of minimizing user confusion) interaction solution, the Whobar model could make practical the reproduction of that sequence across sites.