public function getToken()
  {

    if ($this->has('token'))
    {
      return $this->get('token');
    }

    if ($this->has('access_token'))
    {
      return $this->get('access_token');
    }

    if ($this->has('accessToken'))
    {
      return $this->get('accessToken');
    }

    if ($authorization = $this->getHeader('AUTHORIZATION'))
    {
      return $authorization;
    }

    return null;
  }