You can click on the Google or Yahoo buttons to sign-in with these identity providers,
or you just type your identity uri and click on the little login button.
Notably when some characters such as '?' or '/' are part of a value.
Unless someone shouts, I plan to fix this by disabling Rest urls which could pose problem and using the raw eid in those cases.
Ticket #1219835 - latest update on 2010/08/26, created on 2010/08/11