Sample code for Firebase Auth

firebase-auth-backend.js

import {auth, credential, initializeApp} from "firebase-admin";

// Call this before starting the server
export function init() {
    const serviceAccount = {
        clientEmail: process.env.FIREBASE_SERVICE_ACCOUNT_CLIENT_EMAIL,
        privateKey: process.env.FIREBASE_SERVICE_ACCOUNT_PRIVATE_KEY,
        projectId: process.env.FIREBASE_SERVICE_ACCOUNT_PROJECT_ID
    };

    initializeApp({
        credential: credential.cert(serviceAccount),
        databaseURL: ''
    });
}

// Call this to verify the ID token. Returns a Promise with the UserRecord, or throws if invalid.
export async function decodeIdToken(idToken) {
    const decodedIdToken = await auth().verifyIdToken(idToken);
    return auth().getUser(decodedIdToken.uid);
}

firebase-auth-frontend.js

import firebase from "firebase/app";
import "firebase/auth";

// Call this right when you want to enforce login.
// This will check if the user is logged in, and redirect to the logi screen if they are not.
export function initAuth() {
    return new Promise((resolve, reject) => {
        const config = {
            apiKey: "",
            authDomain: "",
            databaseURL: "",
            projectId: "",
            storageBucket: "",
            messagingSenderId: "",
        };
        firebase.initializeApp(config);

        const unsubscribe = firebase.auth().onAuthStateChanged(function (user) {
            if (!user) {
                // User is not signed in.
                try {
                    resolve(firebase.auth().signInWithRedirect(new firebase.auth.GoogleAuthProvider()));
                } catch (e) {
                    reject(e);
                }
            } else {
                unsubscribe();
                resolve();
            }
        });
    });
}
  
// Call this function to get an ID token that you can send with your requests (in a header)
// to be able to authenticate the user on the backend.
export async function getIdToken() {
    const currentUser = firebase.auth().currentUser;

    return currentUser ? currentUser.getIdToken() : null;
}