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

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 my Firebase Database client-side.
I'm trying to use this tutorial but cannot get it working without using a database secret (which is being depreciated) in makeToken(). I'd prefer to use a service account as reflected in this tutorial. When I look at the difference between the tokens generated, the first 2 pieces separated by a '.' are identical, the last piece after the final '.' is different. The lengths are the same as well. eg:
//Example Generated by Database Secret: TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBv.ZGdlLCBleGNlZWRzIHRoZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4=.dGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2U=
//Example Generated by Service Account: TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBv.ZGdlLCBleGNlZWRzIHRoZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4=.IHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbml=
I can generate the OAuth access token, pass it to FirebaseApp and generate an authentication token, but when it is passed client-side and I attempt to authenticate I get an error: Login Failed! Error: INVALID_TOKEN: Failed to validate MAC.
It seems like there is a lot of misinformation and conflicting information on how this should be done.
I have a getFirebaseService() function server-side that uses Apps Script OAuth2 Library to get an access token.
function getFirebaseService() {
return OAuth2.createService('Firebase')
// Set the endpoint URL.
.setTokenUrl('https://accounts.google.com/o/oauth2/token')
// Set the private key and issuer.
.setPrivateKey(fb_PRIVATE_KEY) //Service account private key
.setIssuer(fb_SERVICE_EMAIL) //Service account email
// Set the property store where authorized tokens should be persisted.
.setPropertyStore(PropertiesService.getScriptProperties())
// Set the scopes.
.setScope('https://www.googleapis.com/auth/userinfo.email https://www.googleapis.com/auth/firebase.database');
}
I have a makeToken() function server-side that gets an authentication token from Firebase using the OAuth access token. I am able to use the service.getAccessToken() OAuth token server-side to access and store data. So that works, I guess my issue is creating a client auth token that's more restrictive.
function makeToken(){
var service = getFirebaseService();
if (service.hasAccess()) {
return FirebaseApp.getDatabaseByUrl(fb_URL, service.getAccessToken()) //Database Secret Works: "AAslhfi3MYACCESSTOKEN2930hf03ah4th8" but is being depreciated.
.createAuthToken(Session.getActiveUser().getEmail());
} else {
Logger.log("makeToken: " + service.getLastError());
}
}
Then client-side, from the sidebar, I try to authenticate with a custom auth token retrieved server-side from makeToken().
var userAuthToken;
google.script.run.withSuccessHandler(function (requestAuthToken) {
userAuthToken = authenticateClient(requestAuthToken)
}).makeToken();
function authenticateClient(userRequestToken) {
var ref = new Firebase(fb_URL);
ref.authWithCustomToken(userRequestToken, function (error, authData) {
if (error) {
console.log("FB Login Failed!", error); //Error below come from here.
}
else {
console.log("FB Login Succeeded!", authData);
}
});
return ref.authData.auth;
}
This results in Login Failed! Error: INVALID_TOKEN: Failed to validate MAC..
Edit: Is it possible FirebaseApp is incorrectly generating the JWT Authentication Token?
Edit2: I think the above edit is unlikely as I attempted to use the GSApp library and had the same issue. It only seems to want the depreciated database secret, not a service account OAuth.

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.