Why authorization differs from authentication in Express - See It in Action

Why Authorization Differs from Authentication in Express

📖 Scenario: You are building a simple Express server that handles user login and access control. You want to understand the difference between authentication (checking who the user is) and authorization (checking what the user can do).

🎯 Goal: Create a basic Express app that authenticates a user by checking a username and password, then authorizes access to a protected route based on the user's role.

📋 What You'll Learn

Create an object called users with usernames as keys and objects containing password and role as values

Create a variable called loggedInUser initialized to null

Write a function called authenticate that takes username and password and sets loggedInUser if credentials match

Write a function called authorize that takes a role and returns true if loggedInUser has that role

Add an Express route /dashboard that uses authorize to allow access only if the user is an admin

💡 Why This Matters

🌍 Real World

Web apps need to know who users are (authentication) and what they can do (authorization) to protect sensitive data and actions.

💼 Career

Understanding authentication and authorization is essential for backend developers building secure web services with Express.

1

Set up user data

Create an object called users with these exact entries: 'alice' with password 'wonderland' and role 'admin', and 'bob' with password 'builder' and role 'user'.

Express

# Create the users object with alice and bob
# Your code here

Hint

Use an object with usernames as keys and objects with password and role as values.

2

Add login state variable

Create a variable called loggedInUser and set it to null to represent no user logged in yet.

Express

const users = {
  alice: { password: 'wonderland', role: 'admin' },
  bob: { password: 'builder', role: 'user' }
};

// Create loggedInUser variable
# Your code here

Hint

Use let to allow changing the logged in user later.

3

Write authentication function

Write a function called authenticate that takes username and password. If the username exists in users and the password matches, set loggedInUser to the user object; otherwise, set it to null.

Express

const users = {
  alice: { password: 'wonderland', role: 'admin' },
  bob: { password: 'builder', role: 'user' }
};

let loggedInUser = null;

// Write authenticate function
# Your code here

Hint

Check if the username exists and password matches, then update loggedInUser.

4

Add authorization and protected route

Write a function called authorize that takes a role and returns true if loggedInUser has that role. Then create an Express app with a route /dashboard that sends 'Welcome admin' if authorized as admin, otherwise sends 'Access denied'.

Express

const users = {
  alice: { password: 'wonderland', role: 'admin' },
  bob: { password: 'builder', role: 'user' }
};

let loggedInUser = null;

function authenticate(username, password) {
  if (users[username] && users[username].password === password) {
    loggedInUser = users[username];
  } else {
    loggedInUser = null;
  }
}

// Write authorize function and Express app with /dashboard route
# Your code here

Hint

Use loggedInUser.role to check authorization. Create an Express route that sends different responses based on authorization.

Practice

1. In Express apps, what is the main difference between authentication and authorization?

easy

A. Authentication checks what the user can access; authorization verifies who they are.

B. Authentication verifies who the user is; authorization checks what they can access.

C. Authentication and authorization both check user identity only.

D. Authorization is done before authentication in Express.

Solution

1. Step 1: Understand authentication purpose

   Authentication confirms the user's identity, like logging in.

2. Step 2: Understand authorization purpose

   Authorization decides what resources or actions the authenticated user can access.

3. Final Answer:

   Authentication verifies who the user is; authorization checks what they can access. -> Option B

4. Quick Check:

   Authentication = identity, Authorization = permissions [OK]

Hint: Authentication = who, Authorization = what they can do [OK]

Common Mistakes:

• Confusing authentication with authorization
• Thinking both check the same thing
• Assuming authorization happens before authentication

2. Which Express middleware is typically used for authentication?

easy

A. passport.authenticate()

B. cors()

C. express.json()

D. express.static()

Solution

1. Step 1: Identify authentication middleware

   Passport.js is a popular Express middleware for handling authentication.

2. Step 2: Check other options

   express.static serves files, express.json parses JSON, cors handles cross-origin requests, none handle authentication.

3. Final Answer:

   passport.authenticate() -> Option A

4. Quick Check:

   passport.authenticate() = authentication middleware [OK]

Hint: Passport is for authentication in Express [OK]

Common Mistakes:

• Choosing express.static for authentication
• Confusing cors with authentication
• Not knowing passport middleware

3. Consider this Express route snippet:

app.get('/dashboard', (req, res) => {
  if (!req.user) {
    return res.status(401).send('Not authenticated');
  }
  if (!req.user.isAdmin) {
    return res.status(403).send('Not authorized');
  }
  res.send('Welcome Admin');
});

What status code will be sent if a logged-in user is not an admin?

medium

A. 200

B. 401

C. 403

D. 500

Solution

1. Step 1: Check authentication condition

   The code checks if req.user exists; if not, sends 401 (unauthenticated).

2. Step 2: Check authorization condition

   If user exists but isAdmin is false, sends 403 (forbidden, unauthorized).

3. Final Answer:

   403 -> Option C

4. Quick Check:

   Authenticated but not authorized = 403 [OK]

Hint: 401 = no login, 403 = no permission [OK]

Common Mistakes:

• Mixing 401 and 403 status codes
• Assuming 200 is sent without admin rights
• Ignoring the authorization check

4. This Express middleware aims to protect routes:

function checkAdmin(req, res, next) {
  if (!req.user.isAdmin) {
    res.status(401).send('Unauthorized');
  }
  next();
}

What is the bug here?

medium

A. req.user might be undefined causing an error

B. Should send status 403 instead of 401 for authorization failure

C. Missing call to next() inside the if block

D. Middleware should be async

Solution

1. Step 1: Analyze req.user usage

   The code accesses req.user.isAdmin without checking if req.user exists, risking a runtime error.

2. Step 2: Check other issues

   While 403 is better for authorization failure, the main bug is possible crash from undefined req.user.

3. Final Answer:

   req.user might be undefined causing an error -> Option A

4. Quick Check:

   Always check req.user exists before properties [OK]

Hint: Check req.user exists before isAdmin [OK]

Common Mistakes:

• Ignoring possible undefined req.user
• Confusing 401 and 403 status codes
• Not returning after sending response

5. You want to protect an Express route so only authenticated users with role 'editor' or 'admin' can access it. Which middleware logic correctly implements this authorization check?

hard

A. if (req.user && req.user.role === 'admin') { next(); } else { res.status(403).send('Forbidden'); }

B. if (!req.user && (req.user.role === 'editor' || req.user.role === 'admin')) { next(); } else { res.status(401).send('Unauthorized'); }

C. if (req.user.role === 'editor' || req.user.role === 'admin') { next(); } else { res.status(401).send('Unauthorized'); }

D. if (!req.user || (req.user.role !== 'editor' && req.user.role !== 'admin')) { res.status(403).send('Forbidden'); } else { next(); }

Solution

1. Step 1: Check authentication and authorization together

   The middleware must first confirm req.user exists (authenticated), then check if role is 'editor' or 'admin'.

2. Step 2: Analyze each option

   if (!req.user || (req.user.role !== 'editor' && req.user.role !== 'admin')) { res.status(403).send('Forbidden'); } else { next(); } correctly denies access if no user or role not allowed, sending 403 Forbidden. Others have logic errors or wrong status codes.

3. Final Answer:

   if (!req.user || (req.user.role !== 'editor' && req.user.role !== 'admin')) { res.status(403).send('Forbidden'); } else { next(); } -> Option D

4. Quick Check:

   Check user exists AND role allowed for authorization [OK]

Hint: Check user exists AND role matches before next() [OK]

Common Mistakes:

• Not checking if user is authenticated first
• Using wrong status codes (401 vs 403)
• Incorrect logical operators in role check