JWT token generation and verification in Node.js - Mini Project: Build & Apply

JWT Token Generation and Verification

📖 Scenario: You are building a simple authentication system for a web app. You need to create and verify JWT tokens to securely identify users.

🎯 Goal: Build a Node.js script that generates a JWT token for a user and then verifies it to confirm the user's identity.

📋 What You'll Learn

Create a user object with exact properties

Define a secret key string for signing tokens

Generate a JWT token using the user object and secret key

Verify the JWT token using the secret key

💡 Why This Matters

🌍 Real World

JWT tokens are widely used in web apps to securely identify users without storing session data on the server.

💼 Career

Understanding JWT token generation and verification is essential for backend developers working on authentication and authorization.

1

Create the user data object

Create a constant called user with these exact properties: id set to 123, username set to 'alice', and role set to 'admin'.

Node.js

// Create the user object with id, username, and role
// Your code here

Hint

Use const user = { id: 123, username: 'alice', role: 'admin' }; to create the user object.

2

Define the secret key

Create a constant called secretKey and set it to the string 'mysecretkey'.

Node.js

const user = { id: 123, username: 'alice', role: 'admin' };
// Define the secret key string
// Your code here

Hint

Use const secretKey = 'mysecretkey'; to define the secret key.

3

Generate the JWT token

Import the jsonwebtoken package and create a constant called token by signing the user object with secretKey using jwt.sign().

Node.js

const user = { id: 123, username: 'alice', role: 'admin' };
const secretKey = 'mysecretkey';
// Import jsonwebtoken and generate token
// Your code here

Hint

Use const jwt = require('jsonwebtoken'); to import and const token = jwt.sign(user, secretKey); to create the token.

4

Verify the JWT token

Create a constant called verifiedUser by verifying the token with secretKey using jwt.verify().

Node.js

const jwt = require('jsonwebtoken');
const user = { id: 123, username: 'alice', role: 'admin' };
const secretKey = 'mysecretkey';
const token = jwt.sign(user, secretKey);
// Verify the token
// Your code here

Hint

Use const verifiedUser = jwt.verify(token, secretKey); to verify the 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