PHP and .htaccess authentication

I just got done reading the online docs concerning http authentication and tried out a script that appears on the page. Apparently it is easy enough to protect any page with http authentication after you have already forced someone to enter a username and password on a regular .htaccess prompting under Apache. What I need to try to accomplish is checking a username and password against a MySQL database and redirect to a different directory upon success. The directory would be protected via a .htaccess file. Is there a way to pass through a .htaccess file if they have already passed a previous authentication scheme as above? Thanks, Ed