Pub/Sub on Android via Google Sign-in

I'd like to use Pub/Sub in my Android app. The main problem is that I can't use creds.json in the project. Instead I'd like to use authenification/authorization like I do it when I use the Gmail API. Maybe somebody knows how to do that or can say me that it is imposible.

Let me explain what I have and what I'd like to have.

I have an email client that uses Gmail API to work with messages. I use Google Sign for authentication.

For now, to check for new messages I use CoroutineWorker that uses PeriodicWorkRequest for execution.

Based on docs Periodic work has a minimum interval of 15 minutes. But I'd like to receive updates more frequently and don't do a lot of requests.

I've found that Gmail API can use Push Notifications.

I've done the preparation and I'm able to get updates via Pub/Sub functionality. My Android app can subscribe for updates.

The worked code looks like this

implementation ('com.google.cloud:google-cloud-pubsub:1.123.7')
implementation 'io.grpc:grpc-okhttp:1.54.0'

GlobalScope.launch(Dispatchers.IO) {
      try {
        val subscriptionName = ProjectSubscriptionName.of("myproject", "my-sub")
        val subscriber = Subscriber.newBuilder(subscriptionName,
          MessageReceiver { message, _ ->
            Log.d("PUBSUB", "message = ${message?.data?.toStringUtf8()}")
          })
          .setCredentialsProvider {
            GoogleCredentials.fromStream(resources.openRawResource(R.raw.creds))
          }
          .build()
        subscriber?.startAsync()?.awaitRunning()
        subscriber?.awaitTerminated()
      } catch (t: Throwable) {
        t.printStackTrace()
        Log.i("PUBSUB", t.message ?: "Something went wrong")
      }
    }

Subscribing to Cloud Pub/Sub via Android devices would be considered an anti-pattern. As you noted, the authentication model is not conducive to using Google sign-on for authenticating. Additionally, the limits on number of resources in Pub/Sub (10,000 subscriptions per topic or per project) mean that you'd only be able to support that many devices/users.

Instead, you'd want to connect the Pub/Sub subscription to Firebase Cloud Messaging to send the notifications to the end user devices. You can trigger a function when a message is published to a topic and then send a notification to a device.