Programmatic authentication to application with federated login in Java

[Martin Dvorak]

I switched my application from 'Google Accounts API' authentication to 'Federated Login'. My application has a REST-style interface and therefore I need to authenticate programmatically. 

It seems that it's not that easy:

  http://blog.notdot.net/2010/06/Using-remote-api-with-OpenID-authentication

Does anyone have a Java client (code) that is able to authenticate?

Any help or suggestions will be appreciated!