session_start(); if(isset($_SESSION['isLoggedIn']) && $_SESSION['isLoggedIn'] === true) { // user is authenticated, allow access to sensitive information } else { // user is not authenticated, redirect to login page header('Location: login.php'); exit; }In this example, we start a new PHP session and check if the 'isLoggedIn' variable is set to true. If it is, then we allow the user access to the sensitive information. If not, we redirect the user to the login page. PHP Auth Check is not a package or library, but rather a built-in function in PHP that can be used in any PHP application.