Last week, I checked in a new module
authtwitter in simpleSAMLphp. You can update and use it right away.
It uses the new OAuth authentication API of Twitter that was released April 15th (two weeks ago).
The twitter authentication module re-uses the simpleSAMLphp OAuth module, and add some special functions to get information from Twitter.
I added support for logging in to Foodle through Twitter.
What I see more and more, is how difficult it is to make UI for the user to select BOTH where the user comes from AND what kind of authentication method he/she wants to use. The result may be that I extend the SAML 2.0 Discovery protocol even more than I have done already, to allow the UI on the discovery service to include an OpenID field, and as well list some other authentication providers.