Passport.js integration in NestJS - Mini Project: Build & Apply

Passport.js Integration in NestJS

📖 Scenario: You are building a simple NestJS application that needs user authentication. You will integrate Passport.js to handle user login using a local strategy.

🎯 Goal: Build a NestJS module that integrates Passport.js with a local strategy for user authentication. You will create the user data, configure Passport, implement the authentication logic, and complete the module setup.

📋 What You'll Learn

Create a user data array with exact users

Add a configuration variable for the local strategy name

Implement Passport local strategy using the user data

Complete the AuthModule with Passport integration

💡 Why This Matters

🌍 Real World

User authentication is essential for most web applications. Passport.js is a popular library to handle authentication strategies in Node.js frameworks like NestJS.

💼 Career

Understanding Passport.js integration in NestJS is valuable for backend developers working on secure user login systems.

1

Create user data array

Create a constant array called users with these exact user objects: { userId: 1, username: 'john', password: 'changeme' } and { userId: 2, username: 'maria', password: 'guess' }.

NestJS

# Your code here

Hint

Define a constant array named users with two user objects exactly as shown.

2

Add local strategy name configuration

Create a constant string called LOCAL_STRATEGY_NAME and set it to 'local'.

NestJS

const users = [
  { userId: 1, username: 'john', password: 'changeme' },
  { userId: 2, username: 'maria', password: 'guess' }
];

# Your code here

Hint

Define a constant string LOCAL_STRATEGY_NAME with the value 'local'.

3

Implement Passport local strategy

Create a class called LocalStrategy that extends PassportStrategy with Strategy from passport-local. Implement a validate method that takes username and password, finds the matching user in users, and returns the user if the password matches. If no user or wrong password, throw UnauthorizedException.

NestJS

const users = [
  { userId: 1, username: 'john', password: 'changeme' },
  { userId: 2, username: 'maria', password: 'guess' }
];

const LOCAL_STRATEGY_NAME = 'local';

# Your code here

Hint

Extend PassportStrategy with Strategy and implement validate to check username and password against users.

4

Complete AuthModule with Passport integration

Create a NestJS module class called AuthModule that imports PassportModule with defaultStrategy set to LOCAL_STRATEGY_NAME. Add LocalStrategy to the providers array and export PassportModule.

NestJS

import { Injectable, UnauthorizedException } from '@nestjs/common';
import { PassportStrategy } from '@nestjs/passport';
import { Strategy } from 'passport-local';
import { Module } from '@nestjs/common';
import { PassportModule } from '@nestjs/passport';

const users = [
  { userId: 1, username: 'john', password: 'changeme' },
  { userId: 2, username: 'maria', password: 'guess' }
];

const LOCAL_STRATEGY_NAME = 'local';

@Injectable()
export class LocalStrategy extends PassportStrategy(Strategy, LOCAL_STRATEGY_NAME) {
  constructor() {
    super();
  }

  async validate(username: string, password: string) {
    const user = users.find(u => u.username === username);
    if (!user || user.password !== password) {
      throw new UnauthorizedException();
    }
    return user;
  }
}

# Your code here

Hint

Create a NestJS module named AuthModule that imports PassportModule with the local strategy, provides LocalStrategy, and exports PassportModule.

Practice

1. What is the main purpose of integrating Passport.js in a NestJS application?

easy

A. To handle user authentication and login strategies

B. To manage database connections

C. To style the frontend components

D. To optimize server performance

Solution

1. Step 1: Understand Passport.js role

   Passport.js is a library designed to handle user authentication in Node.js applications.

2. Step 2: Connect Passport.js with NestJS

   In NestJS, Passport.js is used to define login strategies and verify users securely.

3. Final Answer:

   To handle user authentication and login strategies -> Option A

4. Quick Check:

   Passport.js = Authentication [OK]

Hint: Passport.js is for login and user verification [OK]

Common Mistakes:

• Confusing Passport.js with database tools
• Thinking Passport.js styles UI
• Assuming Passport.js improves server speed

2. Which of the following is the correct way to apply a Passport.js local strategy in a NestJS controller?

easy

A. @UseGuards('local')

B. @UseGuards(LocalStrategy)

C. @UseGuards(AuthGuard('local'))

D. @UseGuards(PassportLocal)

Solution

1. Step 1: Recall NestJS guard syntax

   Passport strategies are applied using AuthGuard with the strategy name as a string.

2. Step 2: Match correct syntax

   The correct syntax is @UseGuards(AuthGuard('local')) to apply the local strategy guard.

3. Final Answer:

   @UseGuards(AuthGuard('local')) -> Option C

4. Quick Check:

   UseGuards with AuthGuard('strategy') [OK]

Hint: Use AuthGuard with strategy name string [OK]

Common Mistakes:

• Passing strategy class instead of string
• Omitting AuthGuard wrapper
• Using incorrect decorator syntax

3. Given this NestJS Passport.js setup, what will be the output when a user with correct credentials logs in?

async validate(username: string, password: string) {
  if (username === 'user' && password === 'pass') {
    return { userId: 1, username };
  }
  return null;
}

medium

A. Returns undefined

B. Throws an error

C. Returns null always

D. Returns user object { userId: 1, username: 'user' }

Solution

1. Step 1: Analyze validate method logic

   The method checks if username is 'user' and password is 'pass'. If yes, it returns a user object.

2. Step 2: Determine output for correct credentials

   For correct credentials, it returns { userId: 1, username } which is { userId: 1, username: 'user' }.

3. Final Answer:

   Returns user object { userId: 1, username: 'user' } -> Option D

4. Quick Check:

   Correct credentials return user object [OK]

Hint: Correct credentials return user object, else null [OK]

Common Mistakes:

• Assuming it throws error on failure
• Confusing null with undefined
• Ignoring the return statement

4. Identify the error in this NestJS Passport.js guard usage:

@UseGuards(AuthGuard(LocalStrategy))
@Get('profile')
getProfile() {
  return 'User Profile';
}

medium

A. AuthGuard should receive strategy name as string, not class

B. Missing @Controller decorator

C. getProfile method must be async

D. AuthGuard cannot be used with @Get

Solution

1. Step 1: Check AuthGuard parameter

   AuthGuard expects a string with the strategy name, e.g., 'local', not the strategy class.

2. Step 2: Confirm correct usage

   Correct usage is @UseGuards(AuthGuard('local')), passing the strategy name as a string.

3. Final Answer:

   AuthGuard should receive strategy name as string, not class -> Option A

4. Quick Check:

   AuthGuard('strategyName') not class [OK]

Hint: Pass strategy name string to AuthGuard [OK]

Common Mistakes:

• Passing strategy class instead of string
• Forgetting to import AuthGuard
• Assuming method must be async

5. You want to protect a NestJS route so only logged-in users can access it using Passport.js. Which combination correctly sets this up?

1. Create a JWT strategy class
2. Use @UseGuards(AuthGuard('jwt')) on the route
3. Implement validate() method in strategy
4. Call AuthGuard('local') on the route

Which steps should you follow?

hard

A. All steps 1, 2, 3, and 4

B. Steps 1, 2, and 3 only

C. Steps 1 and 4 only

D. Steps 2 and 4 only

Solution

1. Step 1: Understand JWT strategy usage

   To protect routes with JWT, create a JWT strategy and implement validate() to verify tokens.

2. Step 2: Apply AuthGuard with 'jwt'

   Use @UseGuards(AuthGuard('jwt')) on routes to enforce JWT authentication.

3. Step 3: Exclude local strategy for JWT protection

   Using AuthGuard('local') is for login, not for protecting routes after login.

4. Final Answer:

   Steps 1, 2, and 3 only -> Option B

5. Quick Check:

   JWT strategy + AuthGuard('jwt') + validate() [OK]

Hint: Use JWT strategy and AuthGuard('jwt') to protect routes [OK]

Common Mistakes:

• Using local strategy guard to protect routes
• Skipping validate() method in strategy
• Applying AuthGuard without strategy name