// Start the session session_start(); // Check if the user has already logged in if(isset($_SESSION['user_id'])) { header("location: dashboard.php"); //redirect to the dashboard page } // If the form has been submitted, validate the user's credentials if ($_SERVER['REQUEST_METHOD'] == 'POST') { // Authenticate the user (example implementation) $username = $_POST['username']; $password = $_POST['password']; // If the user is authenticated, store their user ID in the session and redirect to the dashboard page if (authenticate_user($username, $password)) { $_SESSION['user_id'] = $user_id; header("location: dashboard.php"); } else { $error_message = "Invalid login credentials."; } } // Output the login form echo ''; In this example, `session_start()` is called at the beginning of the script to start the session. The script checks whether the user has already logged in by checking if their `user_id` is stored in the session. If the user has not yet logged in, the script displays a login form. The form is submitted via POST to the same script. If the user's credentials are valid, their `user_id` is stored in the session and they are redirected to the dashboard page. The package library used in this example is the PHP built-in session library. Overall, PHP session login is a widely-used and effective method for managing user authentication and access control in web applications. By using PHP session, developers can easily manage user access and persist login credentials across multiple pages.