JWT authentication flow in Astro - Mini Project: Build & Apply

JWT Authentication Flow in Astro

📖 Scenario: You are building a simple website using Astro where users can log in and access protected content. To keep users logged in securely, you will use JSON Web Tokens (JWT) to manage authentication.

🎯 Goal: Create a basic JWT authentication flow in Astro. You will set up user data, configure a secret key, generate a JWT token for a user, and finally verify the token to allow access to protected content.

📋 What You'll Learn

Create a user object with exact username and password

Define a secret key string for signing JWT tokens

Generate a JWT token using the user data and secret key

Verify the JWT token and extract the user information

💡 Why This Matters

🌍 Real World

JWT authentication is widely used in web apps to securely manage user sessions without storing passwords on the client.

💼 Career

Understanding JWT flows is essential for frontend and backend developers working on secure user authentication systems.

1

Set up user data

Create a constant object called user with these exact properties: username set to "astroUser" and password set to "astroPass123".

Astro

// Your code here

Hint

Use const user = { username: "astroUser", password: "astroPass123" } to create the user object.

2

Define the JWT secret key

Create a constant string called JWT_SECRET and set it exactly to "superSecretKey123".

Astro

const user = {
  username: "astroUser",
  password: "astroPass123"
};

// Your code here

Hint

Use const JWT_SECRET = "superSecretKey123"; to define the secret key.

3

Generate a JWT token

Import sign from jsonwebtoken. Then create a constant called token by signing the user object with JWT_SECRET and set the token to expire in 1 hour using { expiresIn: '1h' }.

Astro

import { sign } from 'jsonwebtoken';

const user = {
  username: "astroUser",
  password: "astroPass123"
};

const JWT_SECRET = "superSecretKey123";

// Your code here

Hint

Use sign(user, JWT_SECRET, { expiresIn: '1h' }) to create the token.

4

Verify the JWT token

Import verify from jsonwebtoken. Then create a function called verifyToken that takes a parameter token and returns the result of verifying the token with JWT_SECRET. Use a try-catch block to return null if verification fails.

Astro

import { sign, verify } from 'jsonwebtoken';

const user = {
  username: "astroUser",
  password: "astroPass123"
};

const JWT_SECRET = "superSecretKey123";

const token = sign(user, JWT_SECRET, { expiresIn: '1h' });

// Your code here

Hint

Use verify(token, JWT_SECRET) inside a try-catch to safely verify the token.

Practice

1. What is the main purpose of a JWT (JSON Web Token) in authentication?

easy

A. To securely transmit user identity and permissions between client and server

B. To store user passwords on the client side

C. To encrypt all user data in the database

D. To replace cookies for storing session data only

Solution

1. Step 1: Understand JWT role in authentication

   JWTs carry encoded user identity and permissions safely between client and server.

2. Step 2: Compare options with JWT purpose

   Only To securely transmit user identity and permissions between client and server correctly describes JWT's role; others confuse JWT with password storage or encryption.

3. Final Answer:

   To securely transmit user identity and permissions between client and server -> Option A

4. Quick Check:

   JWT purpose = secure token for identity [OK]

Hint: JWTs carry user info safely between client and server [OK]

Common Mistakes:

• Thinking JWT stores passwords
• Confusing JWT with database encryption
• Assuming JWT replaces cookies entirely

2. Which of the following is the correct way to send a JWT token in an HTTP request header?

easy

A. Authorization: Bearer <token>

B. Token: JWT <token>

C. Auth-Token: <token>

D. JWT-Authorization: Bearer <token>

Solution

1. Step 1: Recall standard JWT header format

   The standard way to send JWT is in the Authorization header with 'Bearer' prefix.

2. Step 2: Match options to standard

   Only Authorization: Bearer <token> matches the correct syntax: 'Authorization: Bearer <token>'. Others use incorrect header names or formats.

3. Final Answer:

   Authorization: Bearer <token> -> Option A

4. Quick Check:

   JWT header = Authorization: Bearer token [OK]

Hint: JWTs go in 'Authorization: Bearer <token>' header [OK]

Common Mistakes:

• Using wrong header names like 'Token' or 'Auth-Token'
• Omitting 'Bearer' prefix
• Adding extra words like 'JWT' before token

3. Given this Astro server code snippet handling JWT verification, what will be the output if the token is invalid?

import jwt from 'jsonwebtoken';

export async function get({ request }) {
  const authHeader = request.headers.get('Authorization');
  if (!authHeader) return new Response('No token', { status: 401 });

  const token = authHeader.split(' ')[1];
  try {
    const user = jwt.verify(token, 'secretkey');
    return new Response(`User: ${user.name}`, { status: 200 });
  } catch {
    return new Response('Invalid token', { status: 403 });
  }
}

medium

A. Response with status 200 and user name

B. Response with status 401 and message 'No token'

C. Response with status 403 and message 'Invalid token'

D. Response with status 500 and server error message

Solution

1. Step 1: Analyze token verification flow

   If token is invalid, jwt.verify throws an error caught by catch block.

2. Step 2: Check catch block response

   The catch block returns status 403 with message 'Invalid token'.

3. Final Answer:

   Response with status 403 and message 'Invalid token' -> Option C

4. Quick Check:

   Invalid token triggers 403 response [OK]

Hint: Invalid JWT triggers catch block with 403 response [OK]

Common Mistakes:

• Assuming invalid token returns 401
• Confusing catch block with success path
• Expecting server error instead of 403

4. Identify the bug in this Astro JWT authentication snippet:

export async function get({ request }) {
  const authHeader = request.headers.get('Authorization');
  if (!authHeader) return new Response('No token', { status: 401 });

  const token = authHeader.split(' ')[0];
  try {
    const user = jwt.verify(token, 'secretkey');
    return new Response(`User: ${user.name}`, { status: 200 });
  } catch {
    return new Response('Invalid token', { status: 403 });
  }
}

medium

A. Missing secret key in jwt.verify call

B. Token extraction uses wrong index from split

C. No check for missing Authorization header

D. Response status codes are reversed

Solution

1. Step 1: Check how token is extracted

   Token is extracted using authHeader.split(' ')[0], which gets 'Bearer' instead of the token.

2. Step 2: Identify correct token index

   The token is at index 1 after splitting by space, so index 0 is wrong.

3. Final Answer:

   Token extraction uses wrong index from split -> Option B

4. Quick Check:

   Token index must be 1, not 0 [OK]

Hint: Token is after 'Bearer', so use split index 1 [OK]

Common Mistakes:

• Using split index 0 instead of 1
• Forgetting to check Authorization header
• Mixing up status codes 401 and 403

5. You want to implement a refresh token flow in Astro using JWT. Which approach correctly handles token expiration and refresh securely?

hard

A. Send access token only once at login and never refresh it; rely on long expiration time

B. Store both access and refresh tokens in localStorage and refresh access token automatically on every request

C. Store refresh token in localStorage and access token in URL query parameters for easy access

D. Store access token in memory and refresh token in HttpOnly cookie; use refresh token to get new access token when expired

Solution

1. Step 1: Understand secure token storage

   Access tokens should be stored in memory to reduce exposure; refresh tokens in HttpOnly cookies to prevent JavaScript access.

2. Step 2: Use refresh token to get new access token

   When access token expires, client uses refresh token securely to request a new access token.

3. Final Answer:

   Store access token in memory and refresh token in HttpOnly cookie; use refresh token to get new access token when expired -> Option D

4. Quick Check:

   Secure refresh flow = memory + HttpOnly cookie [OK]

Hint: Keep refresh token HttpOnly, access token in memory [OK]

Common Mistakes:

• Storing tokens in localStorage (XSS risk)
• Never refreshing tokens (causes logout)
• Putting tokens in URL (exposes tokens)