Next.js 15 Fullstack (App Router + Server Actions) · レッスン

JWT戦略の実装

JSON Web Tokens（JWT）を統合してステートレス認証を実装し、トークンの生成と検証を学びます。

「JWT戦略の実装」はCoddyKit上の無料Next.js 15 Fullstack (App Router + Server Actions)レッスンです。これはレッスン2/6です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはNext.js 15 Fullstack (App Router + Server Actions)学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Next.js 15 Fullstack (App Router + Server Actions)コースには全6レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

What is a JSON Web Token (JWT)?

Welcome! In this lesson, we'll dive into JSON Web Tokens (JWTs), a popular method for securing APIs.

JWTs are compact, URL-safe means of representing claims to be transferred between two parties.
They are often used for stateless authentication, meaning the server doesn't need to store session information.
This makes APIs more scalable and easier to manage, especially in distributed systems.

JWT's Three Main Parts

A JWT is essentially a long string, but it's structured into three distinct parts, separated by dots (.):

Header: Contains metadata about the token itself (e.g., type of token, signing algorithm).
Payload: Contains the actual claims or data about the user and additional properties.
Signature: Used to verify the token's integrity and authenticity.

Each part is Base64Url-encoded.

Header & Payload in Detail

Let's look closer at the first two parts:

Header: Typically contains two fields:"alg" (algorithm, e.g., HS256) and "typ" (type, which is JWT).
Payload: This is where you put your data, known as 'claims'. Common claims include:
- sub (subject): Usually the user ID.
- exp (expiration time): When the token expires.
- iat (issued at): When the token was issued.
- Custom claims: Any other data you need, like "username" or "role".

The Cryptographic Signature

The signature is the crucial third part that ensures security:

It's created by taking the encoded header, the encoded payload, a secret key, and the algorithm specified in the header.
This combination is then cryptographically hashed.
Why is it important? If anyone tries to tamper with the header or payload, the signature verification will fail, indicating the token is invalid or has been altered.
The secret key must be kept confidential on the server side!

NestJS and JWTs

NestJS provides excellent support for integrating JWTs, leveraging the power of the jsonwebtoken library under the hood.

We'll primarily use the @nestjs/jwt package, which offers a JwtModule and JwtService to handle token generation and verification seamlessly within your application.

First, you'll need to install the package if you haven't already:

npm install @nestjs/jwt passport-jwt --save

Configuring the JwtModule

To use JWTs in NestJS, you need to import and configure the JwtModule in your application's module (e.g., AppModule or a dedicated AuthModule).

The most important option is the secret key, which is used to sign and verify tokens.

import { Module } from '@nestjs/common';
import { JwtModule } from '@nestjs/jwt';

@Module({
  imports: [
    JwtModule.register({
      secret: 'yourSuperSecretKey',
      signOptions: { expiresIn: '60s' }, // e.g., 60s, 7d, 1h
    }),
  ],
  // ... other providers, controllers
})
export class AppModule {}

Generating a JWT in NestJS

Once JwtModule is configured, you can inject JwtService into your services to generate (sign) new tokens. The sign() method takes a payload (usually an object) and creates the JWT string.

import { Injectable } from '@nestjs/common';
import { JwtService } from '@nestjs/jwt';

@Injectable()
export class AuthService {
  constructor(private jwtService: JwtService) {}

  async signIn(user: any): Promise<string> {
    const payload = { username: user.username, sub: user.userId };
    return this.jwtService.sign(payload); // Signs with configured secret & options
  }
}

Code Demo: Token Generation

Let's see how a token is generated conceptually. This example uses the underlying jsonwebtoken library directly, similar to how NestJS does it.

Run this code to see a JWT being created:

// To run this, install 'jsonwebtoken':
// npm install jsonwebtoken --save

const jwt = require('jsonwebtoken');

const payload = {
  sub: 'user123',
  username: 'coder_kit'
};

const secret = 'mySuperSecretKey123'; // Keep this secret safe!

// Sign the token with an expiration of 1 hour
const token = jwt.sign(payload, secret, { expiresIn: '1h' });

console.log('--- Generated JWT ---');
console.log(token);
console.log('\nThis token is valid for 1 hour.');

Verifying a JWT in NestJS

When a client sends a JWT, your server needs to verify it. The JwtService.verify() method checks several things:

Is the signature valid (i.e., was it signed with our secret)?
Has the token expired?
Are there any other validation rules specified?

If valid, it returns the decoded payload. If invalid, it throws an error.

import { Injectable } from '@nestjs/common';
import { JwtService } from '@nestjs/jwt';

@Injectable()
export class AuthService {
  constructor(private jwtService: JwtService) {}

  async verifyToken(token: string): Promise<any> {
    try {
      const payload = this.jwtService.verify(token);
      return payload; // Token is valid, return its data
    } catch (error) {
      // Token is invalid or expired
      throw new Error('Invalid or expired token');
    }
  }
}

Code Demo: Token Verification

Here's how token verification works. You can use the token generated in the previous step (or the example provided) and see it being verified.

Remember, the secret used for verification MUST be the same one used for signing!

// To run this, install 'jsonwebtoken':
// npm install jsonwebtoken --save

const jwt = require('jsonwebtoken');

// IMPORTANT: Replace with a REAL token you generated,
// or use this example token (signed with 'mySuperSecretKey123')
const testToken = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJ1c2VyMTIzIiwidXNlcm5hbWUiOiJjb2Rlcl9raXQiLCJpYXQiOjE3MDcwOTMyMTMsImV4cCI6MTcwNzE3OTYxM30.4i-J_q_e_x_a_m_p_l_e_s_i_g_n_a_t_u_r_e_f_o_r_d_e_m_o'; 

const secret = 'mySuperSecretKey123'; // Must match the signing secret!

console.log('--- Attempting to Verify Token ---');
try {
  const decoded = jwt.verify(testToken, secret);
  console.log('Token is VALID!');
  console.log('Decoded Payload:');
  console.log(decoded);
} catch (error) {
  console.error('Token is INVALID or EXPIRED!');
  console.error('Error:', error.message);
}

JWT Concept Check

You've learned about the three main parts of a JWT. Which of the following components is primarily responsible for ensuring the token's integrity (that it hasn't been tampered with)?

Recap: JWT Essentials

Great job! You've covered the fundamentals of JWTs:

What they are: Compact, stateless tokens for authentication.
Their structure: Header, Payload, and Signature.
Key concepts: How the signature protects integrity and the role of the secret key.
NestJS integration: Using @nestjs/jwt to configure, sign, and verify tokens.

Next, we'll explore how to protect routes using Guards and implement role-based access control!

よくある質問

「JWT戦略の実装」レッスンは無料ですか？

はい。「JWT戦略の実装」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Next.js 15 Fullstack (App Router + Server Actions)コースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Next.js 15 Fullstack (App Router + Server Actions)コースには全6レッスンが含まれています。

「JWT戦略の実装」で何を学びますか？

JSON Web Tokens（JWT）を統合してステートレス認証を実装し、トークンの生成と検証を学びます。ブラウザで直接実行するハンズオンコードでNext.js 15 Fullstack (App Router + Server Actions)を演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Next.js 15 Fullstack (App Router + Server Actions)を始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのNext.js 15 Fullstack (App Router + Server Actions)は初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/6です。

「JWT戦略の実装」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このNext.js 15 Fullstack (App Router + Server Actions)レッスンでコードを書いて実行できますか？

はい。すべてのNext.js 15 Fullstack (App Router + Server Actions)レッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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