Forcing htaccess login again

Now im even getting more confused. Ive been doing some more research into the subject, and cant seem to find any answers. All of the PHP documentation about headers() talks about auth via PHP, but doesnt mention anything about htaccess as the auth system. On my main.php screen, this is where the cookie gets set once the user logs in with htaccess. What im trying to do is incorporate a section into (possibly) main.php which forces the htaccess to rerequest login again using my .htpasswd password file as the criteria. Is there some sort of header information which will make the webserver turn around and say..... "Hey, you shouldnt be here anymore, login again and I might think about letting you in" Because once I can get the user logging in again, it will go to the rest of main.php and unset/reset the cookie with the new user. Scratching my head. Chris