def METHOD_NAME(message, session=None):  # pylint: disable=unused-argument
    """Answer to a client telling us its client ID."""
    if "value" not in message.payload:
        message.reply(
            {
                "type": "error",
                "error": {"type": "invalid_data", "description": '"value" is missing'},
            },
            ok=False,
        )
        return
    message.socket.client_id = message.payload["value"]