code: def redirect_to_login(request, login_url=None,
                        redirect_field_name=REDIRECT_FIELD_NAME):
      
      path = request.build_absolute_uri()
      # if the login url is the same scheme and net location then just
      # use the path as the "next" url.
      login_scheme, login_netloc = \
              urlparse(login_url or settings.LOGIN_URL)[:2]
      current_scheme, current_netloc = urlparse(path)[:2]
      if ((not login_scheme or login_scheme == current_scheme) and
              (not login_netloc or login_netloc == current_netloc)):
          path = request.get_full_path()
      from django.contrib.auth.views import \
              redirect_to_login as auth_redirect_to_login
      return auth_redirect_to_login(path, login_url, redirect_field_name)
docs: redirect to login