Google sign-in in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens after a successful Google sign-in with Firebase?

After a user successfully signs in using Google with Firebase Authentication, what is the immediate result in the Firebase system?

A The user receives a Firebase ID token that can be used to authenticate requests to Firebase services.

B The user is automatically added to the Firebase Realtime Database under a 'users' node.

C The user's Google password is stored in Firebase Authentication for future logins.

D Firebase creates a new Google Cloud project for the user.

💡 Hint

Think about what Firebase Authentication provides after sign-in.

Firebase Authentication issues a Firebase ID token after successful sign-in. This token is used to identify the user securely in Firebase services. It does not store passwords or create new projects automatically.

❓ security

intermediate

Which Firebase rule protects user data after Google sign-in?

Which Firebase Realtime Database security rule ensures that only authenticated users can read their own data after signing in with Google?

A "read": "auth != null && auth.uid == $userId"

B "read": "auth.token.email_verified == false"

C "read": "auth == null"

D "read": "true"

💡 Hint

Consider how to restrict data access to the signed-in user only.

The rule "auth != null && auth.uid == $userId" ensures that only authenticated users can read data where their user ID matches the data node. Other options either allow public access or deny access incorrectly.

❓ Configuration

advanced

Which Firebase config is required for Google sign-in to work?

Which configuration step is essential to enable Google sign-in in a Firebase project?

A Add Google API key to Firebase Realtime Database rules.

B Enable Google sign-in provider in Firebase Authentication console and set the correct OAuth client ID.

C Create a Google Cloud Storage bucket named 'google-signin'.

D Set Firebase Hosting URL as the OAuth redirect URI in Google Cloud Console.

💡 Hint

Think about what must be enabled in Firebase Authentication settings.

To use Google sign-in, you must enable the Google provider in Firebase Authentication and configure OAuth credentials properly. Other options are unrelated or incorrect.

❓ Architecture

advanced

How does Firebase handle user sessions after Google sign-in?

After a user signs in with Google, how does Firebase maintain the user's session on the client side?

A Firebase stores the user's Google password in cookies for session persistence.

B Firebase requires the user to sign in again on every page reload.

C Firebase stores the user's ID token and refresh token in local storage to maintain session state.

D Firebase uses server-side sessions only and does not store tokens on the client.

💡 Hint

Consider how web apps keep users signed in without asking for credentials repeatedly.

Firebase Authentication stores ID and refresh tokens securely on the client (usually local storage or indexedDB) to keep users signed in across sessions. It does not store passwords or require repeated sign-ins on reload.

✅ Best Practice

expert

What is the best practice to secure Firebase API keys when using Google sign-in?

Firebase API keys are visible in client apps. What is the best practice to keep your Firebase project secure when using Google sign-in?

A Keep Firebase API keys secret and never include them in client apps.

B Store Firebase API keys in environment variables on the client side.

C Disable Google sign-in to avoid exposing API keys.

D Use Firebase security rules to restrict database and storage access based on authentication and user roles.

💡 Hint

Think about how Firebase protects data despite public API keys.

Firebase API keys are not secret and are safe to include in client apps. The best practice is to use Firebase security rules to control access based on authentication and user roles. Other options are either impossible or insecure.

Practice

1. What is the main purpose of using Google sign-in with Firebase Authentication?

easy

A. To store user data in Google Drive

B. To let users log in easily using their Google accounts

C. To send emails through Gmail automatically

D. To create Google Cloud virtual machines

Solution

1. Step 1: Understand Firebase Authentication

   Firebase Authentication helps users sign in securely to apps.

2. Step 2: Identify Google sign-in role

   Google sign-in allows users to log in using their Google accounts easily.

3. Final Answer:

   To let users log in easily using their Google accounts -> Option B

4. Quick Check:

   Google sign-in = Easy user login [OK]

Hint: Google sign-in means easy login with Google accounts [OK]

Common Mistakes:

• Confusing sign-in with data storage
• Thinking it sends emails automatically
• Assuming it manages cloud machines

2. Which Firebase Authentication code snippet correctly initializes Google sign-in in JavaScript?

easy

A. const provider = new firebase.auth.TwitterAuthProvider();

B. const provider = new firebase.auth.EmailAuthProvider();

C. const provider = new firebase.auth.FacebookAuthProvider();

D. const provider = new firebase.auth.GoogleAuthProvider();

Solution

1. Step 1: Identify correct provider for Google sign-in

   Google sign-in uses GoogleAuthProvider in Firebase Authentication.

2. Step 2: Match code snippet

   The snippet with new firebase.auth.GoogleAuthProvider() is correct.

3. Final Answer:

   const provider = new firebase.auth.GoogleAuthProvider(); -> Option D

4. Quick Check:

   GoogleAuthProvider = Google sign-in [OK]

Hint: Google sign-in uses GoogleAuthProvider class [OK]

Common Mistakes:

• Using EmailAuthProvider for Google sign-in
• Confusing with Twitter or Facebook providers
• Missing 'new' keyword in initialization

3. Given this JavaScript code snippet for Google sign-in, what will be logged if the user successfully signs in?

const provider = new firebase.auth.GoogleAuthProvider();
firebase.auth().signInWithPopup(provider)
  .then((result) => {
    console.log(result.user.email);
  })
  .catch((error) => {
    console.log(error.message);
  });

medium

A. The user's Google email address

B. An error message about sign-in failure

C. The user's Google profile photo URL

D. The user's Google display name

Solution

1. Step 1: Analyze the success callback

   On success, result.user.email is logged.

2. Step 2: Understand what result.user.email contains

   It contains the signed-in user's Google email address.

3. Final Answer:

   The user's Google email address -> Option A

4. Quick Check:

   result.user.email = user email [OK]

Hint: signInWithPopup success logs user email [OK]

Common Mistakes:

• Confusing email with display name or photo URL
• Assuming error message logs on success
• Ignoring the promise success path

4. You wrote this code to sign in with Google but get an error: firebase.auth().signInWithPopup(provider) is not a function. What is the likely cause?

medium

A. The user canceled the sign-in popup

B. Google sign-in is disabled in Firebase console

C. Firebase Authentication SDK is not imported or initialized properly

D. The provider variable is not declared

Solution

1. Step 1: Understand the error message

   The error says signInWithPopup is not a function, meaning Firebase Auth is missing or not loaded.

2. Step 2: Identify common causes

   Not importing or initializing Firebase Authentication SDK causes this error.

3. Final Answer:

   Firebase Authentication SDK is not imported or initialized properly -> Option C

4. Quick Check:

   Missing SDK causes method undefined error [OK]

Hint: Check Firebase Auth SDK import if signInWithPopup missing [OK]

Common Mistakes:

• Assuming Google sign-in disabled causes method error
• Ignoring SDK import errors
• Confusing user cancel with missing function error

5. You want to allow users to sign in with Google and then save their display name and email in Firestore. Which sequence of steps is correct?

hard

A. Enable Google sign-in in Firebase console, sign in with GoogleAuthProvider, then write user info to Firestore

B. Sign in with GoogleAuthProvider, then enable Google sign-in in Firebase console, then write user info

C. Write user info to Firestore first, then enable Google sign-in, then sign in

D. Enable Google sign-in in Firebase console, write user info to Firestore, then sign in

Solution

1. Step 1: Enable Google sign-in in Firebase console

   This step is required before users can sign in with Google.

2. Step 2: Sign in users using GoogleAuthProvider

   After enabling, use Firebase code to sign in users.

3. Step 3: Save user display name and email to Firestore

   Once signed in, write user info to Firestore database.

4. Final Answer:

   Enable Google sign-in in Firebase console, sign in with GoogleAuthProvider, then write user info to Firestore -> Option A

5. Quick Check:

   Enable -> Sign in -> Save data [OK]

Hint: Enable sign-in first, then sign in, then save user data [OK]

Common Mistakes:

• Trying to sign in before enabling Google sign-in
• Saving user data before sign-in
• Changing order of steps incorrectly