Log out a user using server-side sessions

logout.php

<?php
// can't log out if the session isn't started
session_start();
// emptying the session data is useful if your script continues running after logging out
$_SESSION = [];
// set the cookie to expire immediately 
if (ini_get("session.use_cookies")) { 
    $params = session_get_cookie_params(); 
    setcookie(session_name(), '', time() - 42000, 
        $params["path"], $params["domain"], 
        $params["secure"], $params["httponly"] 
    ); 
}
// destroy the session on the server
session_destroy();
exit;