UBB.threads PHP Forum Software Community Forums Resources and Customizing How Do I? Integrating UBB Threads with Drupal

I have gone through the file html.inc.php and seen the function do_login(); can you please tell where this function is being called and in which file. there is a login form which is calling action="/forum/ubbthreads.php" with post method.

can you please explain this login process in some more details
so that i can automate this with some script.