Phone number authentication in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize Firebase phone authentication.

Firebase

const auth = firebase.auth();
auth.[1]('[phone]')

Drag options to blanks, or click blank then click option'

AsignOut

BcreateUserWithEmailAndPassword

CsignInWithPhoneNumber

DsignInWithEmailAndPassword

Attempts:

3 left

💡 Hint

Common Mistakes

Using email authentication methods instead of phone number methods.

Trying to sign out instead of signing in.

The signInWithPhoneNumber method starts phone number authentication.

2fill in blank

medium

Complete the code to confirm the verification code received by the user.

Firebase

confirmationResult.[1](code).then((result) => {
  const user = result.user;
});

Drag options to blanks, or click blank then click option'

Aconfirm

BverifyCode

CsignIn

DsendVerificationCode

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names like sendVerificationCode or verifyCode.

Trying to sign in directly without confirming the code.

The confirm method verifies the code sent to the user's phone.

3fill in blank

hard

Fix the error in the code to set up reCAPTCHA verifier for phone authentication.

Firebase

window.recaptchaVerifier = new firebase.auth.[1]('recaptcha-container');

Drag options to blanks, or click blank then click option'

ARecaptchaVerifierWidget

BRecaptchaVerifier

CRecaptchaVerifierInstance

DRecaptchaVerifierAuth

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect class names that do not exist in Firebase.

Misspelling the class name.

The correct class to create a reCAPTCHA verifier is RecaptchaVerifier.

4fill in blank

hard

Fill both blanks to create a phone auth provider and send a verification code.

Firebase

const phoneProvider = new firebase.auth.[1]();
firebase.auth().[2]('[phone]');

Drag options to blanks, or click blank then click option'

APhoneAuthProvider

BsignInWithPhoneNumber

CverifyPhoneNumber

DsendVerificationCode

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that do not exist on PhoneAuthProvider.

Confusing provider class with authentication methods.

You create a PhoneAuthProvider instance, then call signInWithPhoneNumber to send the code.

5fill in blank

hard

Fill all three blanks to handle phone number sign-in with reCAPTCHA verifier.

Firebase

window.recaptchaVerifier = new firebase.auth.[1]('recaptcha-container');
const phoneNumber = '[phone]';
const appVerifier = window.[2];
firebase.auth().[3](phoneNumber, appVerifier)
  .then((confirmationResult) => {
    window.confirmationResult = confirmationResult;
  });

Drag options to blanks, or click blank then click option'

ARecaptchaVerifier

BrecaptchaVerifier

CsignInWithPhoneNumber

DverifyPhoneNumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong class or variable names for reCAPTCHA verifier.

Calling incorrect methods for phone sign-in.

First, create a RecaptchaVerifier instance. Then get it from window.recaptchaVerifier. Finally, call signInWithPhoneNumber with the phone number and verifier.

Practice

1. What is the main purpose of phone number authentication in Firebase?

easy

A. To sign in users using SMS codes without passwords

B. To store phone numbers in the database

C. To send marketing messages to users

D. To verify email addresses

Solution

1. Step 1: Understand and identify the main purpose of phone number authentication

   It allows users to sign in by receiving a code on their phone via SMS instead of using a password. The main goal is to authenticate users securely and easily using their phone number and SMS code.

2. Final Answer:

   To sign in users using SMS codes without passwords -> Option A

3. Quick Check:

   Phone number authentication = SMS sign-in [OK]

Hint: Phone auth uses SMS codes to sign in, not emails [OK]

Common Mistakes:

• Confusing phone auth with email verification
• Thinking it stores phone numbers only
• Assuming it sends marketing SMS

2. Which Firebase method is used to start phone number authentication by sending an SMS code?

easy

A. signInWithEmailAndPassword()

B. signInWithPhoneNumber()

C. sendPasswordResetEmail()

D. verifyPhoneNumber()

Solution

1. Step 1: Identify the method for phone auth SMS sending and exclude unrelated methods

   Firebase provides signInWithPhoneNumber() to send the SMS code to the user. signInWithEmailAndPassword() is for email login, sendPasswordResetEmail() is for password reset, and verifyPhoneNumber() is not a Firebase client method.

2. Final Answer:

   signInWithPhoneNumber() -> Option B

3. Quick Check:

   Send SMS code = signInWithPhoneNumber() [OK]

Hint: Phone auth starts with signInWithPhoneNumber() [OK]

Common Mistakes:

• Using email sign-in methods for phone auth
• Confusing password reset with phone auth
• Assuming verifyPhoneNumber() is a Firebase method

3. What will happen if you try to sign in with phone number authentication without setting up reCAPTCHA verifier in Firebase web?

medium

A. The phone number will be stored but no SMS sent

B. The SMS code will be sent without any issues

C. The user will be signed in automatically

D. Firebase will throw an error requiring reCAPTCHA verification

Solution

1. Step 1: Understand reCAPTCHA role and predict behavior without it in Firebase phone auth

   Firebase requires reCAPTCHA on web to prevent abuse and verify the user is human before sending SMS. If reCAPTCHA is not set up, Firebase will block the SMS sending and throw an error demanding reCAPTCHA verification.

2. Final Answer:

   Firebase will throw an error requiring reCAPTCHA verification -> Option D

3. Quick Check:

   Missing reCAPTCHA = error thrown [OK]

Hint: Web phone auth needs reCAPTCHA or it errors [OK]

Common Mistakes:

• Assuming SMS sends without reCAPTCHA
• Thinking user signs in automatically
• Believing phone number stores without SMS

4. Given this code snippet, what is the error?

const confirmationResult = await signInWithPhoneNumber(auth, phoneNumber, appVerifier);
const userCredential = await confirmationResult.confirm(code);

medium

A. phoneNumber should be an email string

B. Using confirm() instead of verify() method

C. Missing reCAPTCHA verifier initialization

D. code variable should be a number, not string

Solution

1. Step 1: Check parameters and identify common mistake in signInWithPhoneNumber code

   The third parameter must be a valid reCAPTCHA verifier instance (appVerifier) initialized properly. If appVerifier is not initialized or missing, the code will fail even if confirm() is called correctly.

2. Final Answer:

   Missing reCAPTCHA verifier initialization -> Option C

3. Quick Check:

   Missing appVerifier init = error [OK]

Hint: Always initialize reCAPTCHA verifier before signInWithPhoneNumber() [OK]

Common Mistakes:

• Confusing confirm() with verify() method
• Passing email instead of phone number
• Assuming code must be number type

5. You want to implement phone number authentication in a React app using Firebase. Which sequence correctly describes the steps to sign in a user?

hard

A. Initialize reCAPTCHA verifier -> call signInWithPhoneNumber() -> send SMS -> confirm code -> sign in user

B. Call signInWithPhoneNumber() -> confirm code -> initialize reCAPTCHA verifier -> sign in user

C. Confirm code -> initialize reCAPTCHA verifier -> call signInWithPhoneNumber() -> sign in user

D. Sign in user -> initialize reCAPTCHA verifier -> call signInWithPhoneNumber() -> confirm code

Solution

1. Step 1: Outline the correct sequence for implementing phone auth

   Initialize reCAPTCHA verifier first to prevent abuse and required before sending SMS. Call signInWithPhoneNumber() next to send the code to the user's phone. Confirm the code received by user using confirmationResult.confirm(code) to verify and sign in the user.

2. Final Answer:

   Initialize reCAPTCHA verifier -> call signInWithPhoneNumber() -> send SMS -> confirm code -> sign in user -> Option A

3. Quick Check:

   reCAPTCHA -> send SMS -> confirm code = correct flow [OK]

Hint: Always start with reCAPTCHA, then send SMS, then confirm code [OK]

Common Mistakes:

• Calling signInWithPhoneNumber before reCAPTCHA setup
• Confirming code before SMS sent
• Trying to sign in before confirmation