OTPHP\OTP::filterOptions PHP Method

    protected function filterOptions(array &$options)
    {
        foreach (['algorithm' => 'sha1', 'period' => 30, 'digits' => 6] as $key => $default) {
            if (isset($options[$key]) && $default === $options[$key]) {
                unset($options[$key]);
            }
        }
        ksort($options);
    }