Federated authentication is a decentralized security mechanism not tied to any one particular provider, and OpenID is an open standard which implements federated authentication. With OpenID, users can create an identity (username and password [or alternatives such as biometrics, keyfob, etc.]) at any OpenID provider and be able to use that same identity at any online app which accepts OpenID logins. Google has supported the OpenID 2.0 protocol since 2008 in a variety of products such as Blogger and Google Apps