'The client has requested authentication.  Payload::
string user
string next service
string method
<authentication specific data>
@type packet: L{bytes}'

def ssh_USERAUTH_REQUEST(self, packet):

    (user, nextService, method, rest) = getNS(packet, 3)
    if ((user != self.user) or (nextService != self.nextService)):
        self.authenticatedWith = []
    self.user = user
    self.nextService = nextService
    self.method = method
    d = self.tryAuth(method, user, rest)
    if (not d):
        self._ebBadAuth(failure.Failure(error.ConchError('auth    returned    none')))
        return
    d.addCallback(self._cbFinishedAuth)
    d.addErrback(self._ebMaybeBadAuth)
    d.addErrback(self._ebBadAuth)
    return d
