My modification allows you to use a different Login class to authenticate your users and your admins with the login information contained in the PHPBB database.
The changes you need to make are listed in the txt file. I have included the new login class you will need to add to your lib directory and I also have included a modified copy of the regular login class if you would like to update that as well.
You will also need to modify the SQL database and I have included the mySQL commands that you can use with your database to make those changes.
There are some small changes I found that needed to be made to other files to adapt the Roster Class completely. Those are listed in the txt file too.
If you prefer to use Group Numbers instead of Group Names, that will require a minor tweak of the authorization code in the phpbb_login file.