ACS view can use validate_referral_url instead of is_safe_url

This was lost in the prior merge conflict resolution

Author: sheilatron

djangosaml2/views.py

@@ -355,8 +355,7 @@ def post(self,
         custom_redirect_url = self.custom_redirect(user, relay_state, session_info)
         if custom_redirect_url:
             return HttpResponseRedirect(custom_redirect_url)
-        if not is_safe_url(url=relay_state, allowed_hosts={self.request.get_host()}):
-            relay_state = settings.LOGIN_REDIRECT_URL
+        relay_state = validate_referral_url(request, relay_state)
         logger.debug('Redirecting to the RelayState: %s', relay_state)
         return HttpResponseRedirect(relay_state)