use Digest::MD5 qw(md5_hex);
my $sid=$ARGS{sid};
my $url=$r->uri();
my $ip=$r->connection->remote_ip();
my $basekey="somespecialkeyequalinsiteaandsiteb";
my $vsid=md5_hex("$ip;;$url;;$basekey");
if ($sid eq $vsid) {
   $m->call_next();
}