Pwauth is an authenticator designed to be used with mod_auth_external or
mod_authnz_external and the Apache HTTP Daemon to support reasonably secure web
authentication out of the system password database on most versions of Unix.

What pwauth actually does is very simple. Given a login and a password, it
returns a status code indicating whether it is a valid login/password or not.
It is normally installed as an suid-root program, so other programs (like
Apache or a CGI program) can run it to check if a login/password is valid even
though they don't themselves have read access to the system password database.

USEFUL for apache2-mod_authnz_external and apache2-mod_authz_unixgroup.