code: def get(self, request, provider=None):
          if not settings.CAS_FEDERATE:
              logger.warning("CAS_FEDERATE is False, set it to True to use federation")
              return redirect("cas_server:login")
          renew = bool(request.GET.get('renew') and request.GET['renew'] != "False")
          if self.request.session.get("authenticated") and not renew:
              logger.warning("User already authenticated, dropping federated authentication request")
              return redirect("cas_server:login")
          try:
              provider = FederatedIendityProvider.objects.get(suffix=provider)
              auth = self.get_cas_client(request, provider, renew)
              if 'ticket' not in request.GET:
                  logger.info("Trying to authenticate %s again" % auth.provider.server_url)
                  return HttpResponseRedirect(auth.get_login_url())
              else:
                  ticket = request.GET['ticket']
                  try:
                      if auth.verify_ticket(ticket):
                          logger.info(
                              "Got a valid ticket for %s from %s" % (
                                  auth.username,
                                  auth.provider.server_url
                              )
                          )
                          params = utils.copy_params(request.GET, ignore={"ticket", "remember"})
                          request.session["federate_username"] = auth.federated_username
                          request.session["federate_ticket"] = ticket
                          auth.register_slo(
                              auth.federated_username,
                              request.session.session_key,
                              ticket
                          )
                          url = utils.reverse_params("cas_server:login", params)
                          response = HttpResponseRedirect(url)
                          if request.GET.get("remember"):
                              max_age = settings.CAS_FEDERATE_REMEMBER_TIMEOUT
                              utils.set_cookie(
                                  response,
                                  "remember_provider",
                                  provider.suffix,
                                  max_age
                              )
                          return response
                      else:
                          logger.info(
                              (
                                  "Got an invalid ticket %s from %s for service %s. "
                                  "Retrying authentication"
                              ) % (
                                  ticket,
                                  auth.provider.server_url,
                                  self.service_url
                              )
                          )
                          return HttpResponseRedirect(auth.get_login_url())
                  except SyntaxError as error:
                      messages.add_message(
                          request,
                          messages.ERROR,
                          _(
                              u"Invalid response from your identity provider CAS upon "
                              u"ticket %(ticket)s validation: %(error)r"
                          ) % {'ticket': ticket, 'error': error}
                      )
                      response = redirect("cas_server:login")
                      response.delete_cookie("remember_provider")
                      return response
          except FederatedIendityProvider.DoesNotExist:
              logger.warning("Identity provider suffix %s not found" % provider)
              return redirect("cas_server:login")