Returns the HTTP headers required for request authorization.

    Returns:
      A dictionary containing the required headers.

def GetHTTPHeaders(self):
    """Returns the HTTP headers required for request authorization.

    Returns:
      A dictionary containing the required headers.
    """
    http_headers = self._adwords_client.oauth2_client.CreateHttpHeader()
    if self.enable_compression:
      http_headers['accept-encoding'] = 'gzip'

    http_headers.update(self.custom_http_headers)

    return http_headers