[imp] custom login

[val]

I use Horde 3 and IMP 4,
I tried to make a custom_login script but everytime I logged on , I'm 
redirected to the Imp Login page.

I copied the custom_login.php file in 
http://mydomain.com/webmail/custom_login.php
I changed the lines
define('AUTH_HANDLER', true);
$authentication = 'none';
...
$server_key = 'imap';
...
<form action="http://myhordedomain.com<?php echo 
Horde::applicationUrl('redirect.php') ?>" method="post">

Any ideas?

Val