I am designing a php/mysql website that will have a members are and a separate "forum" section.
Should I just use the forum software as my "login/registration"? If this is the case should I go with VBulletin, Invision, phpBB3 or something different?
Or should I roll my own single sign on hack? Or something completely different?
If you use Invision you don't need to do a SSO hack. They have external authentication plugins. I've hooked Drupal sites into IPB before. There is documentation on it on Invisions website somewhere.
What happened was people went to Drupal > login and they were logged into both Drupal and the forum. If they registered on the forum, it created an account through Drupal. Worked great.
I've integrated Simple Machines Forum into an already authenticated signed-on session.
I used the integrate_login hook - within which I create a user record within SMF (members) table to match that in the host session.
Depends on what you're after and what the main script uses as password encryption. Every bridge that I did made me choose the main sign-in app based on the password encryption, since if you have a script that has MD5 passwords encrypted and another vBulletin you want to connect to, you'd surely go with the main script as the main sign in due to vBulletin's salted password encryption. It's far more easier to register users this way.
@Richard Harrison:
Would you like to describe step-by-step such an integration process? The SMF docs indicate a long way to go to get these things right which kind of scared me away from trying.