Processes an authentication request. If no authenticator is supplied,
        then authentication succeeds.

        @return: C{Deferred}.
        @rtype: C{twisted.internet.defer.Deferred}

def authenticateRequest(self, service_request, username, password, **kwargs):
        """
        Processes an authentication request. If no authenticator is supplied,
        then authentication succeeds.

        @return: C{Deferred}.
        @rtype: C{twisted.internet.defer.Deferred}
        """
        authenticator = self.getAuthenticator(service_request)

        if self.logger:
            self.logger.debug('Authenticator expands to: %r' % authenticator)

        if authenticator is None:
            return defer.succeed(True)

        args = (username, password)

        if hasattr(authenticator, '_pyamf_expose_request'):
            http_request = kwargs.get('http_request', None)
            args = (http_request,) + args

        return defer.maybeDeferred(authenticator, *args)