def _fetch_response_id(self, response):
        """
        :type response: requests.Response

        :rtype: str
        """

        headers = response.headers

        if self.HEADER_RESPONSE_ID_UPPER_CASED in headers:
            return headers[self.HEADER_RESPONSE_ID_UPPER_CASED]

        if self.HEADER_RESPONSE_ID_LOWER_CASED in headers:
            return headers[self.HEADER_RESPONSE_ID_LOWER_CASED]

        return self._ERROR_COULD_NOT_DETERMINE_RESPONSE_ID_HEADER;
:type response: requests.Response

        :rtype: str