Cakephp 1.3 facebook login and check hostname

Cakephp 1.3 facebook login and check hostname

I have this situation where user login via facebook needs to check on the
$_SERVER['HostName'] as in the database user table that keep records of
particular user details might have more than one row. The difference is by
the "hostname" (to differentiate which subdomain from).
In this situation I can login user with facebook without checking hostname
when it comes to hostname I don't know where should I integrate the check
of "hostname".
Any details that is needed to help understand the situation? I have been
looking around for 2 days and no luck on the solution :/