Is there a way to integrate MyBB with Active Directory using a domain controller so folks who are on that domain can use MyBB without having to register? (It would just pull the users/groups from the DC running active directory)
You could probaly set up the file that powers registration to also modify the Active directory database with the username, password, and details of the person registiring.
You could probably create a plugin that registers a hook for member_login. That hook could look up the data from Active Directory and store it in the $users cache.