You need to add your firebase app configuration in the Firebase directory.

Here is an example:

Filename: firebase.config.js Code:

const firebaseConfig = {
  apiKey: "YOUR API KEY",
  authDomain: "YOUR AUTH DOMAIN",
  projectId: "YOUR PROJECT ID",
  storageBucket: "YOUR STORAGE BUCKET",
  messagingSenderId: "YOUR MESSAGING SENDER ID",
  appId: "YOUR APP ID",
};

export default firebaseConfig;

Here is a live url for how that works: https://z4yed-firebase-google-auth.netlify.app/