You can allow users to sign up and log in to your forum using their Facebook account. This is beneficial because you can use your Facebook app to tap into Facebook's huge viral reach, it increases sign ups by 35 to 50% because users know it will be easy to sign up or log in, users will eventually be able to post a status update on Facebook when they post a new topic or reply, it automatically imports their Facebook profile picture, and it automatically logs the user into your forum when they are already logged into Facebook.
Your users will see a Log in with Facebook button on the Log in and Sign Up screens that will allow them to log in or sign up for your forum through Facebook. An account and profile will still be created for them on the forum and they will appear as a normal user. If they already have a forum account, they will be able to connect their existing forum account to their Facebook account.
Facebook Connect can safely be used on private forums since nothing is shared outside of the forum.
You can enable Facebook Connect on your forum by following the instructions below: