You are right. A more complicated scheme would be required for multiple user-id passwords. One method could be to store these user-id pairs in advance in a hash data file, say ../data/user_id, then check the incoming user-id pair against values in the existing hash. For example:

#/usr/bin/perl

use CGI qw(:standard);
use GDBM_File;

use strict;

my $q=new CGI;

#  Assume an existing saved hash %user_id with 'user' as the key and '
+id' as the value
#  created earlier by $user_id{"$user"} = $id and stored in ../data/us
+er_id

my $verify = "../data/user_id";
tie %user_id, 'GDBM_File', $verify, O_RDWR, 0666 or die "Can't tie $ve
+rify:$!";

my $user = $q->param('user');
my $id = $q->param('id');

# Check values from the query string against values in hash
unless (exists $user_id{"$user"} && $user_id{"$user"} = $id) {

     print $q->header, $q->start_html(-title=>'Page not found');
     print h2("This page was not found"), $q->end_html;

      exit;
    }
  
  untie %user_id;  
    
 # Real page code follows
[download]

By now one has other worries, like being sure the hash is locked while a tie is taking place, about how to update and delete values from the hash, about passing a name-password without security, etc.

Better advice might be to learn about SSL and OS/Web Server authentication for the particular target platform.