Firebase Gmail Auth Integration for Android App

I need to integrate Firebase Authentication into my existing Android app, which currently uses Google Billing. The app will include a registration process using Google Sign-In.

Requirements:
- Add Firebase Auth for Google Sign-In
- Create an 'isRegistered' string in Firebase database (values: 0 or 1)
- User data to be stored in Firebase:
- Mobile Number
- Email ID
- Registration Date
- Expiry Date (App registration lasts one year)

Ideal Skills & Experience:
- Proven experience with Firebase Auth
- Strong Android development skills
- Familiarity with Google Sign-In integration
- Knowledge of Firebase Realtime Database or Firestore

Please ensure the app functions as registered only when 'isRegistered' value is 1.