Password protect a page with PHP

gistfile1.php

if (!isset($_SERVER['PHP_AUTH_USER']) || $_SERVER['PHP_AUTH_USER'] != 'username' || $_SERVER['PHP_AUTH_PW'] != 'password') {
    header('WWW-Authenticate: Basic realm="MyProject"');
    header('HTTP/1.0 401 Unauthorized');
    die('Access Denied');
}