def add_headers(self, request, **kwargs):
        """Add any headers needed by the connection. As of v2.0 this does
        nothing by default, but is left for overriding by users that subclass
        the :class:`HTTPAdapter <requests.adapters.HTTPAdapter>`.

        This should not be called from user code, and is only exposed for use
        when subclassing the
        :class:`HTTPAdapter <requests.adapters.HTTPAdapter>`.

        :param request: The :class:`PreparedRequest <PreparedRequest>` to add headers to.
        :param kwargs: The keyword arguments from the call to send().
        """
        pass