Firebase Cloud Messaging - Handling logout

I was working on the same problem, when I had done my logout() from my application. But the problem was that after logging out, I was still getting push notifications from Firebase. I tried to delete the Firebase token. But after deleting the token in my logout() method, it is null when I query for it in my login() method. After working 2 days I finally got a solution.

1. In your logout() method, delete the Firebase token in the background because you can not delete Firebase token from the main thread

   new AsyncTask<Void,Void,Void>() {
       @Override
       protected Void doInBackground(Void... params) {
           try
           {
               FirebaseInstanceId.getInstance().deleteInstanceId();
           } catch (IOException e)
           {
               e.printStackTrace();
           }
           return null;
       }
   
       @Override
       protected void onPostExecute(Void result) {
           // Call your Activity where you want to land after log out
       }
   }.execute();
   

2. In your login() method, generate the Firebase token again.

   new AsyncTask<Void,Void,Void>() {
       @Override
       protected Void doInBackground(Void... params) {
           String token = FirebaseInstanceId.getInstance().getToken();
           // Used to get firebase token until its null so it will save you from null pointer exeption
           while(token == null) {
               token = FirebaseInstanceId.getInstance().getToken();
           }
           return null;
       }
       @Override
       protected void onPostExecute(Void result) {
       }
   }.execute();
   

Okay. So I managed to do some testing and have concluded the following:

1. deleteToken() is the counterpart of getToken(String, String), but not for getToken().

It only works if the Sender ID you are passing is a different Sender ID (not the same ID that can be seen in your google-services.json). For example, you want to allow a different Server to send to your app, you call getToken("THEIR_SENDER_ID", "FCM") to give them authorization to send to your app. This will return a different registration token that corresponds only to that specific sender.

In the future, if you chose to remove their authorization to send to your app, you'll then have to make use of deleteToken("THEIR_SENDER_ID", "FCM"). This will invalidate the corresponding token, and when the Sender attempts to send a message, as the intended behavior, they will receive a NotRegistered error.

2. In order to delete the token for your own Sender, the correct handling is to use deleteInstanceId().

Special mentioning this answer by @Prince, specifically the code sample for helping me with this.

As @MichałK already doing in his post, after calling the deleteInstanceId(), getToken() should be called in order to send a request for a new token. However, you don't have to call it the second time. So long as onTokenRefresh() onNewToken() is implemented, it should automatically trigger providing you the new token.

For short, deleteInstanceId() > getToken() > check onTokenRefresh() onNewToken().

Note: Calling deleteInstanceId() will not only delete the token for your own app. It will delete all topic subscriptions and all other tokens associated with the app instance.

---

Are you positive you're calling deleteToken() properly? The value for audience should be (also seen from my answer that you linked) is "set to the app server's sender ID". You're passing the getId() value which is not the same as the Sender ID (it contains the app instance id value). Also, how are you sending the message (App Server or Notifications Console)?

getToken() and getToken(String, String) returns different tokens. See my answer here.

I also tried FirebaseInstanceId.getInstance().deleteInstanceId(), but then the next time I call FirebaseInstanceId.getInstance.getToken I receive null (it works on the second try).

It's probably because the first time you're calling the getToken(), it's still being generated. It's just the intended behavior.

I guess, after deleteInstanceId I could immediately call getToken() again, but it looks like a hack.

Not really. It's how you'll get the new generated (provided that it is already generated) token. So I think it's fine.

Developers should never unregister the client app as a mechanism for logout or for switching between users, for the following reasons:

• A registration token isn't associated with a particular logged in user. If the client app unregisters and then re-registers, the app can receive the same registration token or a different registration token.

• Unregistration and re-registration may each take up to five minutes to propagate. During this time messages may be rejected due to the unregistered state, and messages may go to the wrong user. To make sure that messages go to the intended user:

• The app server can maintain a mapping between the current user and the registration token.

• The client app can then check to ensure that messages it receives match the logged in user.

this quote is from a deprecated google documentation

But there is reasons to believe this is still true - even if the documentation above is deprecated.

You can observe this here - check out how they do it in this codelab https://github.com/firebase/functions-samples/blob/master/fcm-notifications/functions/index.js

and here https://github.com/firebase/friendlychat-web/blob/master/cloud-functions/public/scripts/main.js

I did a brief research on what would be the most elegant solution to get back the full control (subscribe and unsubscribe to FCM) as before. Enable and disable the FCM after the user logged in or out.

Step 1. - Prevent auto initialization

Firebase now handle the InstanceID and everything else which need to generate a registration token. First of all you need to prevent auto initialization. Based on the official set-up documentation you need to add these meta-data values to your AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<application>

  <!-- FCM: Disable auto-init -->
  <meta-data android:name="firebase_messaging_auto_init_enabled"
             android:value="false" />
  <meta-data android:name="firebase_analytics_collection_enabled"
             android:value="false" />

  <!-- FCM: Receive token and messages -->
  <service android:name=".FCMService">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT"/>
    </intent-filter>
  </service>

</application>

Now you disabled the automatic token request process. At the same time you have an option to enable it again at runtime by code.

Step 2. - Implement enableFCM() and disableFCM() functions

If you enable the auto initialization again then you received a new token immediately, so this is a perfect way to implement the enableFCM() method. All subscribe information assigned to InstanceID, so when you delete it then initiate to unsubscribe all topic. On this way you able to implement disableFCM() method, just turn back off auto-init before you delete it.

public class FCMHandler {

    public void enableFCM(){
        // Enable FCM via enable Auto-init service which generate new token and receive in FCMService
        FirebaseMessaging.getInstance().setAutoInitEnabled(true);
    }

    public void disableFCM(){
        // Disable auto init
        FirebaseMessaging.getInstance().setAutoInitEnabled(false);
        new Thread(() -> {
            try {
                // Remove InstanceID initiate to unsubscribe all topic
                // TODO: May be a better way to use FirebaseMessaging.getInstance().unsubscribeFromTopic()
                FirebaseInstanceId.getInstance().deleteInstanceId();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }).start();
    }

}

Step 3. - FCMService implementation - token and message receiving

In the last step you need to receive the new token and send direct to your server. Other hand you'll receive your data message and just do it what you want.

public class FCMService extends FirebaseMessagingService {

    @Override
    public void onNewToken(String token) {
        super.onNewToken(token);
        // TODO: send your new token to the server
    }

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        super.onMessageReceived(remoteMessage);
        String from = remoteMessage.getFrom();
        Map data = remoteMessage.getData();
        if (data != null) {
            // TODO: handle your message and data
            sendMessageNotification(message, messageId);
        }
    }

    private void sendMessageNotification(String msg, long messageId) {
        // TODO: show notification using NotificationCompat
    }
}

I think this solution is clear, simple and transparent. I tested in a production environment and it's works. I hope it was helpful.