Firebase service account to generate authentication token for client-side use with Google Apps Script

Question

I am having difficulty using the FirebaseApp (a 3rd party API) to generate an authentication token that can be passed to a sidebar and used by the client to login and access

Answer 1

Alright, so after a very long day I figured it out. I'm going to lay out what I ended up using for libraries and what the issue was (see the third library). The main problem was essentially that the tutorial was outdated and no a lot of people use Firebase in apps script.

OAuth2 (Server-side) Link

I didn't have to change anything here! It was working fine and never an issue.

---

FirebaseApp (Server-side) Link

This is a nice library and I stuck with it because it worked well (once I got it there). I had to make a change to my original code that came from the tutorial I mentioned. My code ended up like this and worked:

if (service.hasAccess()) {   
    return FirebaseApp.getDatabaseByUrl(fb_URL, service.getAccessToken()) //get OAuth Token
                      .createAuthToken(Session.getEffectiveUser().getEmail(), null, serviceAccount.client_email, serviceAccount.private_key);
  //... Added the null, private key, and service email parameters.

---

Firebase (Client-side) Link

Alright, so this is where my main issue was -- The tutorial I followed for client-side setup was old. I had to upgrade the code on my own to use the new 3.x version:

<script src="https://www.gstatic.com/firebasejs/5.8.2/firebase.js"></script>

// Initialize Firebase
var config = {
  apiKey: "<Web API Key>",
  authDomain: "<Project ID>.firebaseapp.com",
  databaseURL: "https://<DB URL>.firebaseio.com/"
  };

firebase.initializeApp(config);

With this firebase instance I was able to update my original authenticateClient() method:

function authenticateClient(userRequestToken) {
  firebase.auth().signInWithCustomToken(userRequestToken).catch(function(error) {
    // Handle Errors here.
    console.error("authClient: ", error.code, error.message);
  });

  return {
    uid: firebase.auth().currentUser.uid,
    metadata: {
      lastSignInTime: firebase.auth().currentUser.lastSignInTime
    }
  }; 
}

That's it! I now have a firebase instance with a signed in user via JWT Custom Token! I came across a few people with similar issues an I hope this helps.