public function SetExpirationMinutes($minutes)
    {
        if ($minutes < 5 || $minutes > 60)
            throw new \InvalidArgumentException('Expiration minutes value of "' . $minutes . '" is not between 5 and 60.');

        $expires = new \DateTime();
        $expires->add(new \DateInterval('PT' . $minutes . 'M'));
        $this->ExpirationTime = $expires->format(DATE_RFC3339);
    }