JWT token generation and verification in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the JWT library.

Node.js

const jwt = require('[1]');

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

Ajsonwebtoken

Bexpress

Chttp

Dcrypto

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'express' instead of 'jsonwebtoken'.

Using 'crypto' which is for cryptography but not JWT.

The jsonwebtoken package is used to generate and verify JWT tokens in Node.js.

2fill in blank

medium

Complete the code to generate a JWT token with a secret key.

Node.js

const token = jwt.sign({ userId: 123 }, '[1]');

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

A12345

BtokenSecret

CmySecretKey

DjwtKey

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number instead of a string as the secret key.

Leaving the secret key empty.

The secret key is a string used to sign the token securely. Here, 'mySecretKey' is used as an example.

3fill in blank

hard

Fix the error in the code to verify a JWT token using the secret key.

Node.js

const decoded = jwt.verify(token, '[1]');

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

Ajwt

Btoken

Csecret

DmySecretKey

Attempts:

3 left

💡 Hint

Common Mistakes

Using the token itself as the secret key.

Using a different or undefined secret key.

The jwt.verify function requires the same secret key used to sign the token to decode it correctly.

4fill in blank

hard

Fill both blanks to generate a token with an expiration time of 1 hour.

Node.js

const token = jwt.sign({ id: user.id }, '[1]', { expiresIn: '[2]' });

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

AmySecretKey

B2h

C1h

D3600

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong expiration format like '2h' or a number without quotes.

Forgetting to add the expiresIn option.

The secret key is needed to sign the token, and the expiresIn option sets the token to expire in 1 hour using '1h'.

5fill in blank

hard

Fill all three blanks to decode a token safely with error handling.

Node.js

try {
  const decoded = jwt.[1](token, '[2]');
  console.log(decoded.[3]);
} catch (err) {
  console.error('Invalid token');
}

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

Averify

BmySecretKey

CuserId

Dsign

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'sign' instead of 'verify' to decode.

Using a wrong secret key.

Accessing a wrong property from decoded token.

Use verify to decode the token with the secret key 'mySecretKey'. Then access the userId property from the decoded token.

Practice

1. What is the main purpose of a JWT token in a Node.js application?

easy

A. To securely transmit user identity without sending passwords repeatedly

B. To store user passwords in the database

C. To encrypt all user data on the server

D. To create a permanent session without expiration

Solution

1. Step 1: Understand JWT token purpose

   JWT tokens are used to prove user identity securely without sending passwords every time.

2. Step 2: Compare options

   Only To securely transmit user identity without sending passwords repeatedly correctly describes this purpose; others describe unrelated or incorrect uses.

3. Final Answer:

   To securely transmit user identity without sending passwords repeatedly -> Option A

4. Quick Check:

   JWT purpose = Secure identity proof [OK]

Hint: JWT = identity proof without password resend [OK]

Common Mistakes:

• Thinking JWT stores passwords
• Confusing JWT with encryption of all data
• Assuming JWT creates permanent sessions

2. Which of the following is the correct syntax to generate a JWT token using the jsonwebtoken library in Node.js?

easy

A. jwt.generate(payload, secretKey, { expiresAt: '1h' })

B. jwt.create(payload, secretKey, { expiresIn: '1h' })

C. jwt.sign(payload, secretKey, { expiresIn: '1h' })

D. jwt.make(payload, secretKey, { expire: '1h' })

Solution

1. Step 1: Recall jsonwebtoken method for token creation

   The correct method to create a token is jwt.sign with payload, secret, and options.

2. Step 2: Check option syntax

   Only jwt.sign(payload, secretKey, { expiresIn: '1h' }) uses jwt.sign and correct option key expiresIn; others use invalid method names or option keys.

3. Final Answer:

   jwt.sign(payload, secretKey, { expiresIn: '1h' }) -> Option C

4. Quick Check:

   Token creation method = jwt.sign [OK]

Hint: Use jwt.sign() with expiresIn option for token creation [OK]

Common Mistakes:

• Using wrong method names like create or generate
• Using expiresAt or expire instead of expiresIn
• Missing the secret key argument

3. Given the code snippet:

const jwt = require('jsonwebtoken');
const token = jwt.sign({ userId: 123 }, 'secret123', { expiresIn: '2h' });
const decoded = jwt.verify(token, 'secret123');
console.log(decoded.userId);

What will be the output when this code runs?

medium

A. 123

B. undefined

C. Error: invalid token

D. null

Solution

1. Step 1: Understand token creation and verification

   The token is created with payload { userId: 123 } and secret 'secret123', then verified with the same secret.

2. Step 2: Check decoded payload output

   jwt.verify returns the original payload if token is valid, so decoded.userId is 123.

3. Final Answer:

   123 -> Option A

4. Quick Check:

   Decoded userId = 123 [OK]

Hint: Verify with same secret returns original payload [OK]

Common Mistakes:

• Expecting undefined or null instead of payload
• Using different secret causing invalid token error
• Not understanding jwt.verify returns payload

4. Identify the error in this JWT verification code snippet:

const jwt = require('jsonwebtoken');
const token = jwt.sign({ id: 1 }, 'mysecret');
const decoded = jwt.verify(token, 'wrongsecret');
console.log(decoded.id);

medium

A. Token is expired

B. jwt.sign method is used incorrectly

C. Payload is missing id property

D. Secret key used for verification is incorrect

Solution

1. Step 1: Check token creation and verification secrets

   Token is signed with 'mysecret' but verified with 'wrongsecret', causing verification failure.

2. Step 2: Understand jwt.verify behavior on secret mismatch

   jwt.verify throws an error if secret does not match, so decoded.id is not accessible.

3. Final Answer:

   Secret key used for verification is incorrect -> Option D

4. Quick Check:

   Secret mismatch = verification error [OK]

Hint: Verify with same secret as sign to avoid errors [OK]

Common Mistakes:

• Assuming token expired without expiration set
• Thinking payload lacks id property
• Misusing jwt.sign method syntax

5. You want to generate a JWT token that expires in 30 minutes and includes the user's email and role. Which code snippet correctly does this using the jsonwebtoken library?

hard

A. jwt.sign({ email: user.email, role: user.role }, 'secretKey', { expire: 1800 })

B. jwt.sign({ email: user.email, role: user.role }, 'secretKey', { expiresIn: '30m' })

C. jwt.sign({ email: user.email, role: user.role }, 'secretKey', { expiresAt: '30min' })

D. jwt.sign({ email: user.email, role: user.role }, 'secretKey', { timeout: '30m' })

Solution

1. Step 1: Identify correct payload and expiration option

   The payload includes email and role, and expiration uses expiresIn with '30m' for 30 minutes.

2. Step 2: Validate option keys and values

   Only jwt.sign({ email: user.email, role: user.role }, 'secretKey', { expiresIn: '30m' }) uses correct option key expiresIn and valid time format '30m'; others use invalid keys or formats.

3. Final Answer:

   jwt.sign({ email: user.email, role: user.role }, 'secretKey', { expiresIn: '30m' }) -> Option B

4. Quick Check:

   expiresIn '30m' = 30 minutes expiry [OK]

Hint: Use expiresIn: '30m' for 30-minute token expiry [OK]

Common Mistakes:

• Using expire or expiresAt instead of expiresIn
• Wrong time format like '30min'
• Using timeout option which is invalid