I'm trying to test SSO between zimbra and my company's portail. I succeed in connecting from portail to zimbra with the script below.

However i would also like to connect from zimbra or another site to my portail, but i dont' know if it's possible, and how to do it?

Zimbra and the portail are using the same directory for connection.

PHP Code:
    * Globals. Can be stored in external config.inc.php or retreived from a DB.
    * User's email address and domain. In this example obtained from a GET query parameter. 
    * i.e. preauthExample.php?email=user@domain.com&domain=domain.com
    * You could also parse the email instead of passing domain as a separate parameter
$user $_GET["user"];
$email "{$user}@{$domain}";

"Need preauth key for domain ".$domain);
    * Create preauth token and preauth URL
$preauthURL $WEB_MAIL_PREAUTH_URL."?account=".$email."&by=name&timestamp=".$timestamp."&expires=0&preauth=".$preauthToken;
     * Redirect to Zimbra preauth URL
header("Location: $preauthURL");
Thanks for your help and i apologize for my english if i made mistakes.