I am not sure if its Shibboleth or this extension but: I can't use it on different domains than the default one.
WordPress MU gives me the possibility to use different domains for different blogs. Obviously, the session cookie will only be valid for the domain the session was started. But because with Shibboleth the session only starts on the default domain, I can't reach the other domains backends.
I would like this extension to respect where I came from and use that domain instead.