Best practice about saving FCM tokens to backend with auth

[slavko-lukic]

I ran into small issue when I'm trying to save FCM token to backend but when I have authentication implemented.
I will demonstrate on the example from docs but alter it a bit to show you what I mean.

import React, { useEffect } from 'react';
import messaging from '@react-native-firebase/messaging';

async function saveTokenToDatabase(token) {
  // here we save FCM to database on our server which requires JWT
}

function App() {
  const { isAuthenticated } = useAuth()
  
  useEffect(() => {
    if (!isAuthenticated) return;
  
    // Get the device token
    messaging()
      .getToken()
      .then(token => {
        return saveTokenToDatabase(token);
      });

    // Listen to whether the token changes
    return messaging().onTokenRefresh(token => {
      saveTokenToDatabase(token);
    });
  }, [isAuthenticated]);
}

In example above we don't want to try and save FCM token to backend because request will fail if JWT is not present, so because of that I put guard statement at the beginning of the useEffect to prevent FCM token handling if user is not authenticated.

Problem arises when user logs out which clears the FCM token and logs back in.
Then saveTokenToDatabase gets called twice, first time here:

messaging()
      .getToken()
      .then(token => {
        return saveTokenToDatabase(token);
      });

and second time in onTokenRefresh.

What is the best way to handle this?

[slavko-lukic]

Seems to me that I can remove onTokenRefresh completely because of the way I implemented it, my backend should always have newest token.
What else could trigger onTokenRefresh while my app is open except calling messaging().deleteToken()?
If I delete tokens at logout but request them again at login with getToken() one case should be covered.

[mikehardy]

I think over a long enough period of time the auth token may expire and be auto-refreshed? the FCM token would be the same though I believe