JWT authentication flow in Astro - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the JWT library in an Astro server file.

Astro

import jwt from '[1]';

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

Ajsonwebtoken

Bexpress

Castro

Dcookie-parser

Attempts:

3 left

💡 Hint

Common Mistakes

Importing 'express' instead of 'jsonwebtoken'.

Trying to import 'astro' as JWT library.

The jsonwebtoken library is used to create and verify JWT tokens in Node.js and Astro server files.

2fill in blank

medium

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

Astro

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

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

Averify

Brefresh

Cdecode

Dsign

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'verify' to create a token.

Using 'decode' which only reads token data.

The sign method creates a new JWT token with the given payload and secret.

3fill in blank

hard

Fix the error in verifying a JWT token from a request header.

Astro

const decoded = jwt.[1](req.headers.authorization.split(' ')[1], 'mysecretkey');

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

Asign

Bdecode

Cverify

Dparse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'decode' which does not verify token validity.

Using 'sign' which creates tokens, not verifies.

The verify method checks the token's validity and returns the decoded payload.

4fill in blank

hard

Fill both blanks to extract the token from the Authorization header and verify it.

Astro

const authHeader = req.headers.[1];
const user = jwt.[2](authHeader.split(' ')[1], 'secret');

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

Aauthorization

Bsign

Cverify

Dcookie

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cookie' instead of 'authorization' header.

Using 'sign' instead of 'verify' to check token.

The token is in the 'authorization' header and must be verified with verify.

5fill in blank

hard

Fill all three blanks to create a JWT token, set it as a cookie, and send a response in Astro.

Astro

const token = jwt.[1]({ id: user.id }, 'secret', { expiresIn: '2h' });
const cookieOptions = { httpOnly: true, maxAge: 7200 };
response.headers.set('Set-Cookie', `token=[2]; HttpOnly; Max-Age=[3]`);
return new Response(JSON.stringify({ success: true }), { status: 200 });

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

Asign

Btoken

C7200

Dverify

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'verify' instead of 'sign' to create token.

Setting cookie name incorrectly.

Mismatch between token expiry and cookie max age.

We create the token with sign, set it as a cookie named 'token', and set max age to 7200 seconds (2 hours).

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)