Examples of using mod_auth_external?

This may be a silly question and may be a case of my having missed something in the documentation, but... I cannot seem to find an example of how to use mod_auth_external to verify a username/password with the Unix password file. I have checked that Apache already has this module installed and loaded and it does. I know that I probably need to use the PHP 'exec' command to run pwauth, but what parameters do I pass to pwauth? I can't find any docs that explain this at all! I tried searching the archives of this list and there doesn't seem to be anything that answers my question. If there's a site somewhere with a code sample or two, that's probably all I need to get going. Anyway, hope I was clear enough with my explanation ;-) Regards, Glenn