Yes you can. Try with the following, which is a cleaned-up version of my previous post:

#!/usr/bin/perl -w

#------------------------------------------------------------
# Usage: pwdcheck login password
#------------------------------------------------------------

use strict;
use Authen::PAM;

#----------------------------------------
# isValid ( user, pass ))
# check whether the user/pass combo is valid
#----------------------------------------
sub isValid {
    my ( $login, $pass ) = @_;
    my $pamh;
    pam_start( "passwd", $login,
           sub { ( ( 0, $pass ) x (@_/2), PAM_SUCCESS() ) },
           $pamh );
    my $res = pam_authenticate($pamh) == PAM_SUCCESS();
    pam_end($pamh);
    return $res;
}

my ( $login, $pass ) = @ARGV;
print isValid ( $login, $pass );
[download]

As you can see, by invoking it as unprivileged user as script username password it prints 1 if the login/pass combo is a valid (unix) one, while it waits a couple of seconds and exits silently otherwise. You can use the isValid function in your cgi script without needing root privileges.

Cheers

Antonio