How to access Magento user's session from outside Magento?

<?php
require_once dirname(__FILE__).'/app/Mage.php';
umask(0) ;
$_SESSION['wz']['customer_id']    =    null;
Mage::app();

// Checking for customer session
Mage::getSingleton('core/session', array('name'=>'frontend') );
$session=Mage::getSingleton('customer/session', array('name'=>'frontend') );

$customer_data = Mage::getModel('customer/customer');

if ($session->isLoggedIn()) {
    //echo "Customer is logged in";
    $_SESSION['wz']['customer_id'] = $session->getId();
} else {
    //echo "Customer is NOT logged in ";
    unset($_SESSION['wz']);
    header("Location: error.php?mode=unk_user");
}