Returns the https headers with credentials, if token is used and url is https
        :param url: url to be queried, including scheme
        :return: dict or None

def headers(self, url):
        """
        Returns the https headers with credentials, if token is used and url is https
        :param url: url to be queried, including scheme
        :return: dict or None
        """
        if self._token and url.lower().startswith('https'):
            return {'Authorization': 'Bearer {}'.format(self._token)}
        else:
            return None