...
use constant USER_DATA => '../data/users/';

my $username = param( 'login' ) || '';
my $password = param( 'password' ) || '';

my $userfile = USER_DATA.$username;
my $message = 'Bad password';
open USER, "< $userfile" or display_page( "Your username and password information did not match.  Check to see that you do not have
    Caps Lock on, hit the back button, and try again." ), exit;
my $real_password = <USER>;
close USER;

if ( $password eq $real_password )
{
	$message = "Hello, $username.  You gave me a good password";
}
...