Role-based authorization in NestJS - Mini Project: Build & Apply

Role-based authorization

📖 Scenario: You are building a simple NestJS backend 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 role-based authorization system in NestJS that allows only users with the admin role to access a protected route.

📋 What You'll Learn

Create a roles array to define user roles

Create a variable to hold the current user's role

Use a guard or function to check if the user role matches the required role

Protect a route so only admin role users can access it

💡 Why This Matters

🌍 Real World

Role-based authorization is used in real apps to control who can see or do what, like only managers can approve requests.

💼 Career

Understanding role-based access control is important for backend developers to secure APIs and protect sensitive data.

1

Define user roles array

Create a constant array called roles with the exact strings 'admin' and 'user'.

NestJS

# Create a constant array called roles with 'admin' and 'user'
# Your code here

Hint

Use const roles = ['admin', 'user']; to define the roles array.

2

Set current user role

Create a variable called currentUserRole and set it to the string 'user'.

NestJS

const roles = ['admin', 'user'];
# Create a variable currentUserRole and set it to 'user'
# Your code here

Hint

Use let currentUserRole = 'user'; to set the current user role.

3

Create role check function

Write a function called canAccessAdmin that returns true if currentUserRole is exactly 'admin', otherwise returns false.

NestJS

const roles = ['admin', 'user'];
let currentUserRole = 'user';
# Write function canAccessAdmin to check if currentUserRole is 'admin'
# Your code here

Hint

Use a simple function that compares currentUserRole to 'admin' and returns the result.

4

Protect route with role check

Create a NestJS controller method called getAdminData that returns the string 'Secret admin data' only if canAccessAdmin() returns true. Otherwise, throw an UnauthorizedException. Import UnauthorizedException from @nestjs/common.

NestJS

const roles = ['admin', 'user'];
let currentUserRole = 'user';

function canAccessAdmin() {
    return currentUserRole === 'admin';
}

// Create getAdminData method that returns 'Secret admin data' if canAccessAdmin() is true
// Otherwise throw UnauthorizedException
// Your code here

Hint

Use an if statement to check canAccessAdmin(). Throw UnauthorizedException if false, else return the secret string.

Practice

1. What is the main purpose of role-based authorization in a NestJS application?

easy

A. To handle HTTP request parsing

B. To manage database connections

C. To control access to routes based on user roles

D. To format response data

Solution

1. Step 1: Understand role-based authorization concept

   Role-based authorization restricts access to parts of an app depending on the user's role.

2. Step 2: Identify the purpose in NestJS context

   In NestJS, it controls which users can access certain routes or features based on their roles.

3. Final Answer:

   To control access to routes based on user roles -> Option C

4. Quick Check:

   Role-based authorization = Access control by roles [OK]

Hint: Remember: roles decide who can access what [OK]

Common Mistakes:

• Confusing authorization with authentication
• Thinking it manages database or HTTP parsing
• Mixing up roles with user data formatting

2. Which decorator is commonly used in NestJS to specify roles allowed on a route?

easy

A. @Roles()

B. @UseGuards()

C. @Controller()

D. @Get()

Solution

1. Step 1: Identify role-specifying decorators

   In NestJS, @Roles() decorator marks which roles can access a route.

2. Step 2: Differentiate from other decorators

   @UseGuards() applies guards, @Controller() defines controllers, @Get() defines HTTP GET routes.

3. Final Answer:

   @Roles() -> Option A

4. Quick Check:

   @Roles() sets allowed roles [OK]

Hint: Look for decorator naming roles directly [OK]

Common Mistakes:

• Using @UseGuards() to specify roles directly
• Confusing route decorators with role decorators
• Missing that @Roles() is custom, not built-in

3. Given this code snippet, what will happen when a user with role 'user' accesses the route?

@Roles('admin')
@Get('admin-data')
getAdminData() {
  return 'Secret admin data';
}

medium

A. The user will receive 'Secret admin data'

B. The user will get a 403 Forbidden error

C. The route will return undefined

D. The server will crash with an error

Solution

1. Step 1: Check the role required by the route

   The route requires 'admin' role via @Roles('admin').

2. Step 2: Compare with user's role

   User has role 'user', which does not match 'admin'.

3. Final Answer:

   The user will get a 403 Forbidden error -> Option B

4. Quick Check:

   Role mismatch causes 403 Forbidden [OK]

Hint: If user role ≠ required role, access denied [OK]

Common Mistakes:

• Assuming any role can access
• Thinking route returns undefined on denial
• Expecting server crash on role mismatch

4. Identify the error in this NestJS guard code for role checking:

canActivate(context: ExecutionContext): boolean {
  const request = context.switchToHttp().getRequest();
  const user = request.user;
  const roles = this.reflector.get('roles', context.getHandler());
  if (!roles) {
    return true;
  }
  return roles.includes(user.role);
}

medium

A. Missing async keyword on canActivate

B. Returning true when roles are not defined

C. Using getHandler() instead of getClass() for roles

D. Not checking if user exists before accessing user.role

Solution

1. Step 1: Review user role access

   The code accesses user.role without verifying if user is defined.

2. Step 2: Identify potential runtime error

   If user is undefined, accessing user.role causes an error.

3. Final Answer:

   Not checking if user exists before accessing user.role -> Option D

4. Quick Check:

   Always check user before role access [OK]

Hint: Check user object exists before role check [OK]

Common Mistakes:

• Assuming user is always present
• Confusing getHandler() and getClass() usage
• Thinking async is required for synchronous guard

5. How can you combine role-based authorization with route-level guards to allow access only if the user has either 'admin' or 'manager' role in NestJS?

hard

A. Use @Roles('admin', 'manager') decorator and a RolesGuard that checks for any matching role

B. Use two separate @Roles decorators, one for 'admin' and one for 'manager', on the same route

C. Use @UseGuards(AdminGuard, ManagerGuard) without @Roles decorator

D. Check roles manually inside the controller method without decorators or guards

Solution

1. Step 1: Understand role decorator usage

   @Roles() accepts multiple roles to allow any of them access.

2. Step 2: Use a guard that checks if user role matches any allowed role

   The RolesGuard reads roles from metadata and checks if user role is included.

3. Final Answer:

   Use @Roles('admin', 'manager') decorator and a RolesGuard that checks for any matching role -> Option A

4. Quick Check:

   Multiple roles in @Roles() + guard = flexible access [OK]

Hint: Pass multiple roles in one @Roles() decorator [OK]

Common Mistakes:

• Using multiple @Roles decorators on one route
• Applying multiple guards instead of one flexible guard
• Skipping decorators and guards for manual checks