I've just created cookbook/authbbpress.php which allows users to authenticate on the wiki using their forum username and password. So, for example, I did:
http://claws.za.net/Profiles/Hodge?action=attr and set the edit password to id:hodgestar. Then to edit the page, I login with my forum username and password.
Not quite sure what use cases will arise, but hey it seems to work. :)