public function clearTokens()
    {
        // Start a session.
        if (session_id() == '') {
            session_start();
        }
        if (isset($_SESSION['pop_csrf'])) {
            unset($_SESSION['pop_csrf']);
        }
        if (isset($_SESSION['pop_captcha'])) {
            unset($_SESSION['pop_captcha']);
        }
        return $this;
    }