<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def not_authenticated(self):
 """ Processing non authenticated users :return: * The rendering of ``settings.CAS_LOGIN_TEMPLATE`` with various messages depending of GET/POST parameters * The redirection to :class:`FederateAuth` if ``settings.CAS_FEDERATE`` is ``True`` and the "remember my identity provider" cookie is found :rtype: django.http.HttpResponse """

        if self.service:
            try:
                service_pattern = ServicePattern.validate(self.service)
                if self.gateway and not self.ajax:
                    # clean messages before leaving django
                    list(messages.get_messages(self.request))
                    return HttpResponseRedirect(self.service)

                if settings.CAS_SHOW_SERVICE_MESSAGES:
                    if self.request.session.get("authenticated") and self.renew:
                        messages.add_message(
                            self.request,
                            messages.WARNING,
                            _(u"Authentication renewal required by service %(name)s (%(url)s).") %
                            {'name': service_pattern.name, 'url': self.service}
                        )
                    else:
                        messages.add_message(
                            self.request,
                            messages.WARNING,
                            _(u"Authentication required by service %(name)s (%(url)s).") %
                            {'name': service_pattern.name, 'url': self.service}
                        )
            except ServicePattern.DoesNotExist:
                if settings.CAS_SHOW_SERVICE_MESSAGES:
                    messages.add_message(
                        self.request,
                        messages.ERROR,
                        _(u'Service %s not allowed') % self.service
                    )
        if self.ajax:
            data = {
                "status": "error",
                "detail": "login required",
                "url": utils.reverse_params("cas_server:login",  params=self.request.GET)
            }
            return json_response(self.request, data)
        else:
            if settings.CAS_FEDERATE:
                if self.username and self.ticket:
                    return render(
                        self.request,
                        settings.CAS_LOGIN_TEMPLATE,
                        utils.context({
                            'form': self.form,
                            'auto_submit': True,
                            'post_url': reverse("cas_server:login")
                        })
                    )
                else:
                    if (
                        self.request.COOKIES.get('remember_provider') and
                        FederatedIendityProvider.objects.filter(
                            suffix=self.request.COOKIES['remember_provider']
                        )
                    ):
                        params = utils.copy_params(self.request.GET)
                        url = utils.reverse_params(
                            "cas_server:federateAuth",
                            params=params,
                            kwargs=dict(provider=self.request.COOKIES['remember_provider'])
                        )
                        return HttpResponseRedirect(url)
                    else:
                        # if user is authenticated and auth renewal is requested, redirect directly
                        # to the user identity provider
                        if self.renew and self.request.session.get("authenticated"):
                            try:
                                user = FederatedUser.get_from_federated_username(
                                    self.request.session.get("username")
                                )
                                params = utils.copy_params(self.request.GET)
                                url = utils.reverse_params(
                                    "cas_server:federateAuth",
                                    params=params,
                                    kwargs=dict(provider=user.provider.suffix)
                                )
                                return HttpResponseRedirect(url)
                            # Should normally not happen: if the user is logged, it exists in the
                            # database.
                            except FederatedUser.DoesNotExist:  # pragma: no cover
                                pass
                        return render(
                            self.request,
                            settings.CAS_LOGIN_TEMPLATE,
                            utils.context({
                                'form': self.form,
                                'post_url': reverse("cas_server:federateAuth")
                            })
                        )
            else:
                return render(
                    self.request,
                    settings.CAS_LOGIN_TEMPLATE,
                    utils.context({'form': self.form})
                )