Login with PHPBB on a WordPress Page?

Hi WordPress experts. I’m trying to allow my users to login with PHPBB credentials on WP.

I tried something like this: http://www.3cc.org/blog/2010/03/integrating-your-existing-site-into-phpbb3/

I put common.php from PHPBB in header.php of my WP theme.

But got some errors on WP, not PHPBB though, like make_clickable() already being declared, but just commented it out on WP. Then I got call to function getParameter on null.

To be clear, I am NOT interested in using the WordPress authentication system! None of my users are on the WP account system, and I don’t want them to be. I’m saying I want to build my own form on a template page called page-login.php in WordPress that uses the PHPBB system, and use all PHPBB functions to manipulate the user within the WP theme, not caring about any WP authentications. Then also have the username info show in each page like phpBB. I just need access to all of things I can get from those lines of code shown from that link above like the $user object and $db object.

Like this: https://wiki.phpbb.com/Practical.External_login

Anyone have experience/tips on this? Thanks