Assigning webhooks to Firebase Messaging "subscribe to topic" event

Question

In my current project I am using the Kreait Firebase PHP SDK to send out push notifications to Android & iOS devices that have subscribed to notifications on named topics. No issues thus far. However, rather than have fixed topic names I would now like to generate topic names based on the current "condition" of the connecting device. The condition could, for example, be a geographic location.

This is not too difficult either and I have modified my app to handle this. However, in order to put the ability to have such autogenerated topics to use I need to know the topic names on my server so I can send out targeted messages via Kreait. I find Google's Firebase documentation a bit dense at times and have not been able to establish whether it is possible to assign webhooks that get called by Firebase whenever a SubscribeToTopic, UnsubscribeFromTopic event occurs.

A simple question - does FCM even offer anything like this capability? If so, any pointers to the relevant documentation would be much appreciated.

Answer 1

There is no public API to get a list of topic names from Firebase, nor is there a way to hook into the subscription mechanism.

Your best bet is to simply make two calls when a user subscribes to a topic: one to Firebase, and one to your own backend API that keeps a list of active topics/conditions.