Firebase Authentication is 100% free on the Spark plan — no credit card needed.

1. Go to console.firebase.google.com and click Add project
2. Name it (e.g. "study-friends"), disable Google Analytics if you want, click Create project
3. In the left menu go to Build → Authentication → Get Started
4. Enable these Sign-in providers:
   • Google — toggle on, save
   • Phone — toggle on, save
   • Email/Password — toggle on, save
5. Go to Project Settings (gear icon) → scroll to Your apps → click </> Web
6. Register the app, copy the firebaseConfig object
7. Open StudyFriends.html in a text editor, find the line:
   const FIREBASE_CONFIG = { apiKey: "YOUR_API_KEY", … } and replace it with your copied config
8. For Phone auth to work, add localhost to Authentication → Settings → Authorized domains
9. Save the file and open it in your browser — all login methods will work!