Adding Google/Facebook login to Myth/Auth?

At the moment i am researching on how to extend Myth/Auth with a google/facebook login. But i do not really have a clue on where to start yet, beside some thoughts. I am thinking about changing Myth/Auth helper functions to check if there is a normal login or one where facebook/google is involved. But i am not sure yet if this is the right approach for this....

What would be a good starting point on how to intergrate google/facebook api login into Myth/Auth? Any tips and/or advice is welcome.

Greets,
Hermes