Where can I modify this?
Edit: Nevermind, I found it. There's a folder called Authentication, go figure.
Now I see I can create my own authentication scheme easily by modifying an existing one.
The problem would be setting them per user.
A temporary fix for those importing from another software using vBulletin as an intermediate would be to modify vBulletin.php directly.
I don't think there is an AdminCP option to do this. I assume this is planned but not in the beta?