php simple password cookie with get

<?php
$password="123456";
if (isset($_GET['password'])){
    setcookie("password", $_GET['password']);
    $_COOKIE['password']=$_GET['password'];
}
if (!isset($_COOKIE['password']) || $_COOKIE['password']!=$password) {
    echo 'sorry, you are not allowed to view this...';
    die;
}
?>