How to destroy HTTP authentication (from PHP)?

Hi all, Alright: here's a bit of a "challenge" (so as to avoid the word "issue") ;) my colleagues have run into previously: how to kill HTTP authentication... I remember that they never did figure that one out, and I too will now have to get my hands dirty with trying to find a proper way to do so. Simply unsetting the PHP_AUTH_USER and PHP_AUTH_PWD variables doesn't seem to do any magic, and using a forced 401 ('Unauthorized') HTTP header is also highly ideal (not to say blatantly dirty)... Soooo, has anyone found a proper way of achieving this (ideally from PHP)? Also, in case this cannot be done from PHP, does anyone know of any Apache modules (or tricks/tweaks/settings) that will allow HTTP authentication to be neatly destroyed? Thanks in advance, and cheers, Olafo