How do I make a user's account based on their Facebook account?

I’m developing a multiplayer game that is very social, and I’d like a user to create an account by logging into their Facebook account. In our game there’s no value in creating an account just based on your email and a password, so that is not an option.

With that said, is there a tutorial out there for creating a “Sign up with Facebook” button in your game, and then using their Facebook account to create a game user account?

Also, is there a tutorial for using their Facebook account to invite their friends to the game?

Thank you in advance.

You should take a look at Facebook’s Unity SDK