def METHOD_NAME(self, transport, service):
    """
    Return a class to use as a service for the given transport.
    @type transport:    L{transport.SSHServerTransport}
    @type service:      L{bytes}
    @rtype:             subclass of L{service.SSHService}
    """
    if service == b"ssh-userauth" or hasattr(transport, "avatar"):
        return self.services[service]