Well, what about having a script called check-cookie.pl at every domain? The user clicks a link to go to www.mymaindomain/cgi-bin/comments.pl and that somehow passes off to myfirstdomain/cgi-bin/check-cookie.pl which would include this:

local(@getcookies) = split (/; /,$ENV{'HTTP_COOKIE'});
local(%cookies);
   foreach(@getcookies){
    ($ckey, $cval) = split (/=/,$_);
    $cookies{$ckey} = $cval;
   } #end foreach(@getcookies)

$user_sid = $cookies{'phpbb2mysql_sid'};
$user_logged = $cookies{'phpbb2mysql_data'};
$user_lang = $cookies{'lang'};

if ($user_logged !~ /autologin/) {
print "$user_logged";
    &error(not_logged);
}
[download]

That would check the local cookie on that domain before passing back to the www.mymaindomain/cgi-bin/comments.pl script again. Shouldn't that work?

My only problem now is, how do I pass it off? I have a require line in the comments.pl that takes it to the check-cookie.pl script at myfirstdomain.com, but it doesn't read the cookie.