validate order

[morp]

Hi all,
I'm coding my paymenet module.

I validate my order in this way:

--
$currency = new Currency(intval(isset($_POST['currency_payement']) ? $_POST['currency_payement'] : $cookie->id_currency)); $total = floatval(number_format($cart->getOrderTotal(true, 3), 2, '.', ''));

$cardpayment = new cardpayment();

$cardpayment->validateOrder($cart->id, _PS_OS_PREPARATION_, $total, $cardpayment ->displayName, NULL, NULL, $currency->id);
---

The validation goes well, perfect.


Looking in some payment module, I see that someone validate order in this way, passing a secure key:

--
$order = new Order($cardpayment->currentOrder);

Tools::redirectLink(__PS_BASE_URI__.'order-confirmation.php?
id_cart='.$cart>id.'&id;_module='.$cardpayment->id.'&id;_order='.$cardpayment>currentOrder.'&key;='.$order->secure_key);
--

but, what does it mean? Why I can validate the order without the key? Why should I use it?

please someone can explain me more?


many thanks
bye