Token generation and validation in NestJS - Mini Project: Build & Apply

Token generation and validation

📖 Scenario: You are building a simple authentication system in a NestJS backend. You need to create a token generation and validation mechanism to securely identify users.

🎯 Goal: Build a NestJS service that generates a JWT token for a user ID and validates the token to extract the user ID.

📋 What You'll Learn

Create a service with a method to generate a JWT token using a secret key

Create a method to validate the JWT token and extract the user ID

Use the @nestjs/jwt package for token operations

Use a fixed secret key 'mySecretKey' for signing tokens

Use a payload with a userId property

💡 Why This Matters

🌍 Real World

Token generation and validation is essential for user authentication in web applications, allowing secure access control.

💼 Career

Understanding JWT handling in NestJS is a common requirement for backend developer roles working with modern authentication systems.

1

Setup JWT service and secret key

Create a NestJS service class called AuthService. Inside it, create a private readonly property called jwtSecret and set it to the string 'mySecretKey'.

NestJS

export class AuthService {
  // Your code here
}

Need a hint?

Define a class named AuthService and add a private readonly property jwtSecret with the value 'mySecretKey'.

2

Add token generation method

Inside the AuthService class, add a method called generateToken that takes a parameter userId of type string. Use the sign method from @nestjs/jwt to create a JWT token with a payload containing { userId } and sign it with this.jwtSecret. Return the generated token.

NestJS

export class AuthService {
  private readonly jwtSecret = 'mySecretKey';

  // Your code here
}

Need a hint?

Use the sign function from @nestjs/jwt to create a token with the payload { userId } and sign it using this.jwtSecret.

3

Add token validation method

Inside the AuthService class, add a method called validateToken that takes a parameter token of type string. Use the verify method from @nestjs/jwt to verify the token with this.jwtSecret. Return the userId from the decoded payload.

NestJS

import { sign, verify } from '@nestjs/jwt';

export class AuthService {
  private readonly jwtSecret = 'mySecretKey';

  generateToken(userId: string): string {
    const payload = { userId };
    return sign(payload, { secret: this.jwtSecret });
  }

  // Your code here
}

Need a hint?

Use the verify function from @nestjs/jwt to decode the token and extract the userId.

4

Export AuthService and finalize

Add an export statement to export the AuthService class so it can be used in other parts of the application.

NestJS

import { sign, verify } from '@nestjs/jwt';

export class AuthService {
  private readonly jwtSecret = 'mySecretKey';

  generateToken(userId: string): string {
    const payload = { userId };
    return sign(payload, { secret: this.jwtSecret });
  }

  validateToken(token: string): string {
    const decoded = verify(token, { secret: this.jwtSecret }) as { userId: string };
    return decoded.userId;
  }
}

// Your code here

Need a hint?

Use export { AuthService }; to export the class.