Custom authentication tokens in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a custom token with Firebase Admin SDK.

Firebase

const admin = require('firebase-admin');

admin.initializeApp();

const uid = 'some-uid';
admin.auth().[1](uid)
  .then((customToken) => {
    console.log(customToken);
  })
  .catch((error) => {
    console.log('Error creating custom token:', error);
  });

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

AcreateCustomToken

BgenerateToken

CsignInWithCustomToken

DgetCustomToken

Attempts:

3 left

💡 Hint

Common Mistakes

Using generateToken instead of createCustomToken

Trying to use client SDK methods like signInWithCustomToken on the server

The Firebase Admin SDK uses createCustomToken(uid) to generate a custom authentication token for the given user ID.

2fill in blank

medium

Complete the code to add custom claims to the token.

Firebase

const uid = 'user123';
const additionalClaims = { admin: true };

admin.auth().createCustomToken(uid, [1])
  .then((token) => {
    console.log(token);
  });

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AextraClaims

BadditionalClaims

CcustomClaims

Dclaims

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the claims object with a wrong variable name

Not passing any claims object when needed

The second argument to createCustomToken is an object with additional claims, commonly named additionalClaims.

3fill in blank

hard

Fix the error in the code to verify a custom token on the client side.

Firebase

firebase.auth().[1](customToken)
  .then((userCredential) => {
    console.log('User signed in');
  })
  .catch((error) => {
    console.error(error);
  });

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AauthenticateWithToken

BverifyIdToken

CcreateCustomToken

DsignInWithCustomToken

Attempts:

3 left

💡 Hint

Common Mistakes

Using verifyIdToken which is a server-side method

Using createCustomToken on the client side

On the client side, use signInWithCustomToken(token) to sign in with a custom token.

4fill in blank

hard

Fill both blanks to decode and verify a custom token on the server.

Firebase

admin.auth().[1](idToken)
  .then((decodedToken) => {
    const uid = decodedToken.[2];
    console.log('User ID:', uid);
  })
  .catch((error) => {
    console.error('Error verifying token:', error);
  });

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AverifyIdToken

BdecodeToken

Cuid

DuserId

Attempts:

3 left

💡 Hint

Common Mistakes

Using decodeToken which is not a Firebase Admin method

Accessing userId instead of uid

Use verifyIdToken to verify the token and access the user's ID with decodedToken.uid.

5fill in blank

hard

Fill all three blanks to create a custom token with claims and handle errors properly.

Firebase

const uid = 'user456';
const additionalClaims = { premiumAccount: true };

admin.auth().[1](uid, [2])
  .then((token) => {
    console.log('Token:', token);
  })
  .catch(([3]) => {
    console.error('Failed to create token:', error);
  });

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AcreateCustomToken

Bclaims

Cerror

DadditionalClaims

Attempts:

3 left

💡 Hint

Common Mistakes

Using claims instead of additionalClaims as variable name

Not naming the catch parameter error

Use createCustomToken(uid, additionalClaims) and catch errors with a parameter named error.