Anonymous authentication in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens after anonymous sign-in in Firebase?

When a user signs in anonymously using Firebase Authentication, what is the state of the user's identity immediately after sign-in?

Firebase

firebase.auth().signInAnonymously().then(userCredential => {
  console.log(userCredential.user.uid);
});

A The user is signed out immediately after sign-in.

B The user has a unique user ID but no email or password associated.

C The user is signed in with a Google account by default.

D The user is signed in with a temporary email and password.

💡 Hint

Think about what anonymous means in authentication.

Anonymous sign-in creates a unique user ID without requiring email or password. This allows temporary access without user credentials.

❓ security

intermediate

What is a security risk of anonymous authentication?

Which of the following is a potential security risk when using Firebase anonymous authentication in an app?

A Anonymous authentication requires users to enter a password.

B Anonymous users can access admin-only data by default.

C Users can lose their data if they uninstall the app without linking their account.

D Anonymous users are automatically upgraded to full accounts.

💡 Hint

Consider what happens if the anonymous user identity is lost.

Anonymous users have a unique ID stored locally. If the app is uninstalled, the ID is lost and data linked to that ID is inaccessible.

❓ Configuration

advanced

Which Firebase rule allows anonymous users to read data but not write?

Given Firebase Realtime Database rules, which rule snippet correctly allows anonymous users to read data but prevents them from writing?

A

{
  "rules": {
    ".read": "auth != null",
    ".write": "auth != null && auth.isAnonymous == false"
  }
}

B

{
  "rules": {
    ".read": "auth != null && auth.isAnonymous == true",
    ".write": "auth != null"
  }
}

C

{
  "rules": {
    ".read": "auth == null",
    ".write": "auth == null"
  }
}

D

{
  "rules": {
    ".read": "true",
    ".write": "false"
  }
}

💡 Hint

Check the conditions for read and write permissions based on auth state.

Rule B allows any authenticated user to read, but only non-anonymous users to write. This matches the requirement.

❓ Architecture

advanced

How to preserve user data when upgrading anonymous users?

What is the recommended approach to keep user data when an anonymous Firebase user upgrades to a permanent account?

A Sign out the anonymous user and sign in with the new account without linking.

B Create a new user and manually copy data from the anonymous user ID to the new user ID.

C Delete the anonymous user and create a new permanent user without data migration.

D Link the anonymous user credential to the new permanent credential using linkWithCredential().

💡 Hint

Think about how Firebase supports account linking.

linkWithCredential() merges the anonymous user with the permanent account, preserving data and user ID.

🧠 Conceptual

expert

What is the behavior of Firebase anonymous authentication token expiration?

Which statement correctly describes the token expiration behavior for Firebase anonymous authentication users?

A Anonymous user tokens expire after one hour and are automatically refreshed by the SDK.

B Anonymous user tokens expire immediately after sign-in.

C Anonymous user tokens expire after 24 hours and require manual refresh by the developer.

D Anonymous user tokens never expire and do not require refresh.

💡 Hint

Consider how Firebase handles token lifecycle for all users.

Firebase issues ID tokens valid for one hour for all users, including anonymous ones, and the SDK refreshes them automatically.