session from http to https

[eluser]sampada[/eluser]
Hi,

I am just wondering where I did wrong:

Let's say a users is viewing a sponsorship page and to sponsor a particular child he has to be logged in. So in view page of sponsorship controller I set
$_SESSION['redirect']="rapyd/sponsor".

In auth controller:
Login takes the user to secure domain

function login()
{
....
if (isset($_SESSION['redirect'])){
$redirect = $_SESSION['redirect'];
unset($_SESSION['redirect']);
redirect(keep_lang("$redirect"));
}
else
{
redirect(keep_lang("homepage/index"));
}

}


In config.php

$config['cookie_domain']=".xxx.xxx";



But here the redirect session variable is blank.

Any ideas where I did wrong??