'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}'

def getService(self, transport, service):

    if ((service == 'ssh-userauth') or hasattr(transport, 'avatar')):
        return self.services[service]
