public function isExpired()
    {
        $payload = $this->getPayload();

        if (isset($payload['exp'])) {
            $now = new \DateTime('now');

            if (is_int($payload['exp'])) {
                return ($now->getTimestamp() - $payload['exp']) > 0;
            }

            if (is_numeric($payload['exp'])) {
                return ($now->format('U') - $payload['exp']) > 0;
            }
        }

        return false;
    }