Store the user session for a client.

        :param sid: The session id of the client.
        :param session: The session dictionary.
        :param namespace: The Socket.IO namespace. If this argument is omitted
                          the default namespace is used.

def save_session(self, sid, session, namespace=None):
        """Store the user session for a client.

        :param sid: The session id of the client.
        :param session: The session dictionary.
        :param namespace: The Socket.IO namespace. If this argument is omitted
                          the default namespace is used.
        """
        namespace = namespace or '/'
        eio_session = self.eio.get_session(sid)
        eio_session[namespace] = session