Role-based guards in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the necessary decorator for roles.

NestJS

import { [1] } from '@nestjs/common';

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AController

BUseGuards

CRoles

DSetMetadata

Attempts:

3 left

💡 Hint

Common Mistakes

Using Roles decorator which does not exist by default.

Confusing UseGuards with metadata setting.

The SetMetadata decorator is used to define custom metadata like roles in NestJS.

2fill in blank

medium

Complete the code to create a custom decorator named Roles.

NestJS

export const Roles = (...roles: string[]) => [1]('roles', roles);

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ASetMetadata

BUseGuards

CController

DInjectable

Attempts:

3 left

💡 Hint

Common Mistakes

Using UseGuards instead of SetMetadata.

Trying to use Injectable which is for services.

SetMetadata is used to create custom decorators that attach metadata like roles.

3fill in blank

hard

Fix the error in the guard method to get roles metadata.

NestJS

const roles = this.reflector.get<string[]>([1], context.getHandler());

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A'role'

B'roles'

C'permissions'

D'auth'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'role' instead of 'roles' causes undefined metadata.

Using unrelated keys like 'permissions' or 'auth'.

The metadata key used for roles is 'roles', so it must match exactly.

4fill in blank

hard

Fill in the blank to check if user roles include any required role.

NestJS

if (!roles) return true; // Allow access if no roles are set

return user.roles.some(role => roles.[1](role)); // Check if user has any required role

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Aequals

Bexcludes

Cincludes

Dcontains

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'excludes' which is not a valid array method.

Returning false when no roles are set blocks access incorrectly.

The includes method checks if the user's role is in the required roles array. Returning true if no roles are set allows open access.

5fill in blank

hard

Fill all three blanks to apply the Roles guard to a controller method.

NestJS

@[1](RolesGuard)
@[2]('admin')
@[3]('dashboard')
async getDashboard() {
  return 'Admin Dashboard';
}

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AUseGuards

BRoles

CController

DGet

Attempts:

3 left

💡 Hint

Common Mistakes

Using Controller instead of Get for the route method.

Forgetting to apply UseGuards to activate the guard.

UseGuards applies the guard, Roles sets the required roles, and Get defines the route method.

Practice

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

easy

A. To manage application configuration

B. To handle database connections

C. To format HTTP responses

D. To restrict access to routes based on user roles

Solution

1. Step 1: Understand role-based guard function

   Role-based guards check user roles before allowing access to routes.

2. Step 2: Identify the correct purpose

   Restricting access based on roles matches the guard's role in security.

3. Final Answer:

   To restrict access to routes based on user roles -> Option D

4. Quick Check:

   Role-based guard = restrict access by roles [OK]

Hint: Guards control access; roles limit who can enter [OK]

Common Mistakes:

• Confusing guards with database or config management
• Thinking guards format responses
• Assuming guards handle unrelated tasks

2. Which of the following is the correct way to apply a role-based guard to a route in NestJS?

easy

A. @UseGuards(RolesGuard)\n@Get('profile')

B. @Controller('profile')\n@RolesGuard()

C. @Roles('admin')\n@UseGuards(AuthGuard)

D. @UseGuards(AuthGuard)\n@Get('profile')

Solution

1. Step 1: Identify correct guard usage syntax

   Use @UseGuards with the guard class to apply it to routes.

2. Step 2: Match with role-based guard usage

   @UseGuards(RolesGuard) is correct; @Roles decorator marks roles separately.

3. Final Answer:

   @UseGuards(RolesGuard)\n@Get('profile') -> Option A

4. Quick Check:

   @UseGuards(RolesGuard) applies guard [OK]

Hint: Use @UseGuards with guard class to protect routes [OK]

Common Mistakes:

• Using @RolesGuard() instead of @UseGuards
• Mixing @Roles and @UseGuards incorrectly
• Applying guards without @UseGuards decorator

3. Given this guard code snippet, what will be the result if the user role is 'user' and the route requires 'admin' role?

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

medium

A. Access granted

B. Access denied

C. Runtime error due to missing roles

D. Always returns true

Solution

1. Step 1: Understand role check logic

   The guard checks if the user's role is included in the allowed roles array.

2. Step 2: Apply given roles and user role

   User role is 'user', route requires 'admin', so roles.includes('user') is false.

3. Final Answer:

   Access denied -> Option B

4. Quick Check:

   User role not in allowed roles = deny access [OK]

Hint: Check if user role is in allowed roles array [OK]

Common Mistakes:

• Assuming access is granted if roles differ
• Thinking roles includes user role always
• Ignoring roles array presence

4. Identify the error in this role-based guard implementation:

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

medium

A. Returns false if no roles metadata, blocking all access

B. Missing async keyword causes runtime error

C. Incorrect use of context.getHandler()

D. Should check user permissions instead of roles

Solution

1. Step 1: Analyze roles metadata check

   If roles metadata is missing, the guard returns false blocking access.

2. Step 2: Understand typical behavior for missing roles

   Usually, missing roles means no restriction, so returning false is too strict.

3. Final Answer:

   Returns false if no roles metadata, blocking all access -> Option A

4. Quick Check:

   No roles metadata should allow access, not block [OK]

Hint: Missing roles metadata should not block access by default [OK]

Common Mistakes:

• Assuming missing roles means deny access
• Forgetting to handle undefined roles gracefully
• Confusing async necessity in this context

5. You want to create a role-based guard that allows access if the user has any one of multiple roles specified on a route. Which approach correctly implements this behavior?

hard

A. Use multiple guards each checking one role and combine them with @UseGuards

B. Check only the first role in roles array against user.role in canActivate

C. Use @Roles('admin', 'editor') decorator and check if user.role is included in roles array inside canActivate

D. Ignore roles and allow access to all authenticated users

Solution

1. Step 1: Understand multiple roles in @Roles decorator

   @Roles can accept multiple roles as arguments to specify allowed roles.

2. Step 2: Implement canActivate to check inclusion

   Checking if user.role is in roles array allows access if user has any allowed role.

3. Final Answer:

   Use @Roles('admin', 'editor') decorator and check if user.role is included in roles array inside canActivate -> Option C

4. Quick Check:

   Check user role in roles array for multiple allowed roles [OK]

Hint: Check if user role is in roles array for multiple roles [OK]

Common Mistakes:

• Checking only first role ignores others
• Using multiple guards unnecessarily
• Allowing all authenticated users ignores roles