calling wp_loging

Hi there. I am trying to integrate with ZenCart so that when someone logs into Zencart it also logs them into WordPress. I have made it so that registration between the two work, but I cannot get the wp_login to work.

It seems to just die without an error. Here’s my code:
`function update (&$callingClass, $notifier, $paramsArray) {
global $db;

$email = $_POST[’email_address’];
$user_id = username_exists($email);
if (!$user_id) {
$user_id = email_exists($email);
}
if (!$user_id) {
if ($_POST[‘password’] == ”) {
$user_pass = wp_generate_password();
} else {
$user_pass = $_POST[‘password’];
}
$user_id = wp_create_user( $email, $user_pass, $email );
update_usermeta($user_id,’first_name’,$_POST[‘firstname’]);
update_usermeta($user_id,’last_name’,$_POST[‘lastname’]);
wp_new_user_notification($user_id, $user_pass);

$user = wp_authenticate($email, $user_pass);

if ( !is_wp_error($user) )
return true;
}
}`