Ideally it should be any of the major web sign on methods (fb, google, twitter, linked-in) Github would be cool though. Maybe if we get some time we'll hack that together.
Forget about Facebook, it takes weeks before someone responds to game request and response is usually "Deny request and block app" in best cases and "Unfriend" in others.
I'm sure you're excited to get it out, and you've put a lot of work into this game, but I would consider pulling it for now, and polishing things up a bit more first. First impressions are big. I would also look at Bombermine for inspiration. Just one guy on the internet's opinion.