HTTP authentication with PHP as CGI

According to the PHP manual, the $_SERVER['PHP_AUTH_USER'] and $_SERVER['PHP_AUTH_PW'] variables are not available when PHP is running as CGI. Any ideas how to circumbent this issue? To my understanding, they are passed to Apache and it simply does not provide them to CGI scripts, and when PHP is a module it can get them from there, but not when it is running as CGI.

I know that the user is stored in $_ENV['REMOTE_USER'] as well, but as far as I know the password is not stored anywhere. Perhaps someone has written a module for Apache that can do this? Or maybe something else that I'm missing?