[jlank]

This sounds a lot like SAML (Security Assertion Markup Language) Alpha = IdP, Beta = Service Provider, Gamme = a user or some server requesting access to Beta's data or services. Alpha would contain a set of ACL's (Access Control Lists) that prescribe what groups / users have access to what content or services on B.

http://en.wikipedia.org/wiki/Security_Assertion_Markup_Langu...