Piwik\Plugins\Login\Controller::clearSession PHP Method

    public static function clearSession()
    {
        $authCookieName = Config::getInstance()->General['login_cookie_name'];
        $cookie = new Cookie($authCookieName);
        $cookie->delete();
        Session::expireSessionCookie();
    }

 private function checkPiwikIsNotInstalled()
 {
     if (!SettingsPiwik::isPiwikInstalled()) {
         return;
     }
     \Piwik\Plugins\Login\Controller::clearSession();
     $message = Piwik::translate('Installation_InvalidStateError', array('<br /><strong>', '</strong>', '<a href=\'' . Common::sanitizeInputValue(Url::getCurrentUrlWithoutFileName()) . '\'>', '</a>'));
     Piwik::exitWithErrorMessage($message);
 }