Role-based access control in Express - Mini Project: Build & Apply

Role-based access control

📖 Scenario: You are building a simple Express server for a company. Different users have different roles like 'admin' and 'user'. You want to control access to certain routes based on these roles.

🎯 Goal: Create a basic Express app that uses role-based access control (RBAC) middleware to allow or deny access to routes depending on the user's role.

📋 What You'll Learn

Create an Express app with a users data structure

Add a variable to hold the current user's role

Write middleware to check the user's role before allowing access

Protect routes so only users with the right role can access them

💡 Why This Matters

🌍 Real World

Role-based access control is used in web apps to restrict what users can do based on their roles, like admin or regular user.

💼 Career

Understanding RBAC is important for backend developers to secure APIs and protect sensitive data.

1

Set up users data

Create a constant called users that is an object with these exact entries: alice with role admin, bob with role user, and carol with role guest.

Express

# Your code here

Hint

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

2

Set current user role

Create a variable called currentUserRole and set it to the role of user bob from the users object.

Express

const users = {
  alice: { role: 'admin' },
  bob: { role: 'user' },
  carol: { role: 'guest' }
};

// Your code here

Hint

Access the role property of bob inside users.

3

Create role check middleware

Write a function called checkRole that takes a parameter role and returns a middleware function. This middleware should check if currentUserRole equals the role parameter. If yes, call next(). Otherwise, respond with status 403 and message 'Access denied'.

Express

const users = {
  alice: { role: 'admin' },
  bob: { role: 'user' },
  carol: { role: 'guest' }
};

const currentUserRole = users.bob.role;

// Your code here

Hint

Return a middleware function that compares currentUserRole with the given role.

4

Protect routes with middleware

Create an Express app using express(). Add two routes: /admin protected by checkRole('admin') middleware that sends 'Welcome Admin', and /user protected by checkRole('user') middleware that sends 'Welcome User'.

Express

const users = {
  alice: { role: 'admin' },
  bob: { role: 'user' },
  carol: { role: 'guest' }
};

const currentUserRole = users.bob.role;

function checkRole(role) {
  return function (req, res, next) {
    if (currentUserRole === role) {
      next();
    } else {
      res.status(403).send('Access denied');
    }
  };
}

// Your code here

Hint

Use app.get with the checkRole middleware and send the correct welcome messages.

Practice

1. What is the main purpose of role-based access control (RBAC) in an Express app?

easy

A. To speed up the server response time

B. To limit user actions based on their assigned roles

C. To store user passwords securely

D. To log all user activities automatically

Solution

1. Step 1: Understand RBAC concept

   RBAC means controlling what users can do depending on their role, like admin or guest.

2. Step 2: Identify main purpose in Express

   In Express, RBAC limits access to routes or actions based on user roles to keep the app safe.

3. Final Answer:

   To limit user actions based on their assigned roles -> Option B

4. Quick Check:

   RBAC controls user permissions = A [OK]

Hint: RBAC controls what users can do by role [OK]

Common Mistakes:

• Confusing RBAC with performance optimization
• Thinking RBAC stores passwords
• Assuming RBAC logs activities automatically

2. Which of the following is the correct way to define a middleware function in Express to check if a user has the role 'admin'?

easy

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

B. function checkAdmin(req, res) { if(req.user.role == 'admin') next(); else res.send('Forbidden'); }

C. function checkAdmin(req, res, next) { if(req.user.role = 'admin') next(); else res.status(403).send('Forbidden'); }

D. function checkAdmin(req, res, next) { if(req.user.role !== 'admin') next(); else res.status(403).send('Forbidden'); }

Solution

1. Step 1: Check middleware signature

   Middleware must have three parameters: req, res, next.

2. Step 2: Verify role check and response

   function checkAdmin(req, res, next) { if(req.user.role === 'admin') next(); else res.status(403).send('Forbidden'); } correctly compares role with 'admin' using === and calls next() if true; else sends 403 status.

3. Final Answer:

   function checkAdmin(req, res, next) { if(req.user.role === 'admin') next(); else res.status(403).send('Forbidden'); } -> Option A

4. Quick Check:

   Middleware with correct params and strict role check = D [OK]

Hint: Middleware needs (req, res, next) and strict role check [OK]

Common Mistakes:

• Using assignment (=) instead of comparison (===)
• Missing next() parameter or call
• Wrong logic reversing role check

3. Given this Express route with role check middleware, what will be the response if a user with role 'user' tries to access it?

app.get('/admin', checkAdmin, (req, res) => { res.send('Welcome Admin'); });
function checkAdmin(req, res, next) {
  if(req.user.role === 'admin') next();
  else res.status(403).send('Forbidden');
}

medium

A. 403 Forbidden status with 'Forbidden' message

B. 'Welcome Admin'

C. 500 Internal Server Error

D. 404 Not Found

Solution

1. Step 1: Analyze middleware behavior for role 'user'

   The middleware checks if role is 'admin'. Since role is 'user', condition fails.

2. Step 2: Determine response when role check fails

   Middleware sends 403 status with 'Forbidden' message and does not call next(), so route handler is skipped.

3. Final Answer:

   403 Forbidden status with 'Forbidden' message -> Option A

4. Quick Check:

   Non-admin blocked with 403 Forbidden = B [OK]

Hint: Middleware blocks non-admin with 403, no next() call [OK]

Common Mistakes:

• Assuming route handler runs for non-admin
• Confusing 403 with 404 or 500 errors
• Ignoring middleware role check logic

4. Identify the error in this Express middleware for role-based access control:

function checkRole(req, res, next) {
  if(req.user.role = 'admin') {
    next();
  } else {
    res.status(403).send('Access denied');
  }
}

medium

A. Middleware missing req and res parameters

B. Missing next() call inside the else block

C. Incorrect status code for access denial

D. Using assignment (=) instead of comparison (===) in the if condition

Solution

1. Step 1: Check the if condition syntax

   The condition uses single = which assigns 'admin' to req.user.role instead of comparing it.

2. Step 2: Understand impact of assignment in condition

   Assignment always returns truthy, so else block never runs, causing wrong behavior.

3. Final Answer:

   Using assignment (=) instead of comparison (===) in the if condition -> Option D

4. Quick Check:

   Use === for comparison, not = [OK]

Hint: Use === for comparison, not = assignment [OK]

Common Mistakes:

• Confusing assignment and comparison operators
• Forgetting to call next() in middleware
• Using wrong HTTP status codes

5. You want to protect multiple routes so only users with roles 'admin' or 'manager' can access them. Which middleware implementation correctly allows this in Express?

hard

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

B. function checkRoles(req, res, next) { if(req.user.role === 'admin' || 'manager') next(); else res.status(403).send('Forbidden'); }

C. function checkRoles(req, res, next) { if(['admin', 'manager'].includes(req.user.role)) next(); else res.status(403).send('Forbidden'); }

D. function checkRoles(req, res, next) { if(req.user.role == 'admin' || req.user.role == 'manager') next(); else res.status(404).send('Forbidden'); }

Solution

1. Step 1: Check role inclusion logic

   function checkRoles(req, res, next) { if(['admin', 'manager'].includes(req.user.role)) next(); else res.status(403).send('Forbidden'); } uses array includes() to check if role is 'admin' or 'manager', which is correct and clean.

2. Step 2: Verify status code and logic correctness

   Using && requires role to be both 'admin' and 'manager' simultaneously (impossible); condition like if(role === 'admin' || 'manager') has wrong syntax and always passes since 'manager' is truthy; using 404 instead of 403 for forbidden access is incorrect.

3. Final Answer:

   function checkRoles(req, res, next) { if(['admin', 'manager'].includes(req.user.role)) next(); else res.status(403).send('Forbidden'); } -> Option C

4. Quick Check:

   Use includes() for multiple roles and 403 status = C [OK]

Hint: Use array includes() to check multiple roles cleanly [OK]

Common Mistakes:

• Using incorrect logical operators or syntax
• Checking role equality incorrectly
• Sending wrong HTTP status code for forbidden