def _cbFinishedAuth(self, result):
        """
        The callback when user has successfully been authenticated.  For a
        description of the arguments, see L{twisted.cred.portal.Portal.login}.
        We start the service requested by the user.
        """
        (interface, avatar, logout) = result
        self.transport.avatar = avatar
        self.transport.logoutFunction = logout
        service = self.transport.factory.getService(self.transport,
                self.nextService)
        if not service:
            raise error.ConchError('could not get next service: %s'
                                  % self.nextService)
        log.msg('%r authenticated with %r' % (self.user, self.method))
        self.transport.sendPacket(MSG_USERAUTH_SUCCESS, b'')
        self.transport.setService(service())

        The callback when user has successfully been authenticated.  For a
        description of the arguments, see L{twisted.cred.portal.Portal.login}.
        We start the service requested by the user.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/ssh/userauth.py