Maybe this can help you :
1. Firebase Authentication in App Inventor Using Javascript
2. App Inventor Tutorials and Examples: User Identification | Pura Vida Apps
3. Topic
https://community.thunkable.com/t/free-firebase-authentication-v-3-0-update-link/8543
4. Topic
5. Topic
6. Topic Free Extension
https://community.appybuilder.com/t/firebase-authentication-extensions/507