Adding support for SAML authentication

We have a branch of SsoAuthBundle with support for SAML authentication. We are using CAS authentication, but are gradually switching over to SAML, so we added SAML support in this bundle to make the transition easier.

I'd like to solicit feedback from the community about our implementation and what can be done to make the bundle more agnostic towards other SSO protocols. Right now, the bundle is very CAS centric.