To implement a Node.js Express server with user registration and authentication using JSON Web Tokens (JWT), you'll need to follow these steps:

1. Set up the project
2. Install required packages
3. Configure MongoDB connection
4. Create User model
5. Implement JWT utilities
6. Implement validation checks
7. Create routes for user registration and authentication

Here's a sample implementation:

1. Set up the project:
Create a new directory for your project, navigate into it, and initialize a new Node.js project by running:

```bash
mkdir jwt-auth-server
cd jwt-auth-server
npm init -y
```

2. Install required packages:

```bash
npm install express mongoose bcryptjs jsonwebtoken dotenv cors body-parser
```

3. Configure MongoDB connection:
Create a `.env` file in the root of your project and add your MongoDB connection string:

```
MONGODB_URI=mongodb+srv://username:password@cluster.mongodb.net/database-name?retryWrites=true&w=majority
SECRET_KEY=mysecretkey
```

Replace `username`, `password`, and `database-name` with your actual MongoDB credentials.

4. Create User model (`models/User.js`):

```javascript
const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const UserSchema = new Schema({
  email: { type: String, required: true, unique: true },
  password: { type: String, required: true }
});

module.exports = mongoose.model('User', UserSchema);
```

5. Implement JWT utilities (`utils/jwt.js`):

```javascript
const jwt = require('jsonwebtoken');
const dotenv = require('dotenv');

dotenv.config();

function generateToken(user) {
  return jwt.sign({ id: user._id }, process.env.SECRET_KEY, { expiresIn: '24h' });
}

function verifyToken(token) {
  try {
    return jwt.verify(token, process.env.SECRET_KEY);
  } catch (err) {
    return null;
  }
}

module.exports = { generateToken, verifyToken };
```

6. Implement validation checks (`utils/validation.js`):

```javascript
function isValidEmail(email) {
  const regex = /^[\w-]+(\.[\w-]+)*@([\w-]+\.)+[a-zA-Z]{2,7}$/;
  return regex.test(email);
}

function isStrongPassword(password) {
  // At least one uppercase letter, one lowercase letter, one number and one special character, and at least 8 characters long
  const regex = /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/;
  return regex.test(password);
}

module.exports = { isValidEmail, isStrongPassword };
```

7. Create routes for user registration and authentication (`index.js`):

```javascript
const express = require('express');
const mongoose = require('mongoose');
const bcrypt = require('bcryptjs');
const cors = require('cors');
const bodyParser = require('body-parser');
const dotenv = require('dotenv');

const User = require('./models/User');
const { generateToken, verifyToken } = require('./utils/jwt');
const { isValidEmail, isStrongPassword } = require('./utils/validation');

dotenv.config();

mongoose.connect(process.env.MONGODB_URI, { useNewUrlParser: true, useUnifiedTopology: true, useCreateIndex: true });

const app = express();
app.use(cors());
app.use(bodyParser.json());

app.post('/register', async (req, res) => {
  const { email, password } = req.body;

  if (!isValidEmail(email)) {
    return res.status(400).json({ message: 'Invalid email format' });
  }

  if (!isStrongPassword(password)) {
    return res.status(400).json({ message: 'Weak password. Must have at least one uppercase letter, one lowercase letter, one number, one special character and be at least 8 characters long.' });
  }

  const existingUser = await User.findOne({ email });

  if (existingUser) {
    return res.status(409).json({ message: 'Email already in use' });
  }

  const hashedPassword = await bcrypt.hash(password, 10);
  const user = new User({ email, password: hashedPassword });
  await user.save();

  res.status(201).json({ message: 'User registered successfully', user });
});

app.post('/login', async (req, res) => {
  const { email, password } = req.body;

  const user = await User.findOne({ email });

  if (!user || !(await bcrypt.compare(password, user.password))) {
    return res.status(401).json({ message: 'Invalid email or password' });
  }

  const token = generateToken(user);

  res.json({ message: 'Logged in successfully', token });
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => console.log(`Server running on port ${PORT}`));
```

Now you can run your server using `node index.js` and test the registration and authentication endpoints with tools like Postman or curl.
JSON 웹 토큰(JWT)을 사용하여 사용자 등록 및 인증 기능을 갖춘 Node.js Express 서버를 구현하려면 다음 단계를 따라야 합니다.

1. 프로젝트 설정
2. 필요한 패키지 설치
3. MongoDB 연결 구성
4. 사용자 모델 생성
5. JWT 유틸리티 구현
6. 유효성 검사 구현
7. 사용자 등록 및 인증을 위한 경로 생성

다음은 샘플 구현입니다.

1. 프로젝트 설정하기
프로젝트를 위한 새 디렉터리를 만들고, 그 디렉토리로 이동한 다음, 새 Node.js 프로젝트를 실행하여 초기화합니다:

```bash
mkdir jwt-auth-server
cd jwt-auth-server
npm init -y
```

2. 필요한 패키지를 설치합니다:

```bash
npm install express mongoose bcryptjs jsonwebtoken dotenv cors body-parser
```

3. 프로젝트 루트에 `.env` 파일을 생성하고 MongoDB 연결 문자열을 추가합니다:

```
MONGODB_URI=mongodb+srv://username:password@cluster.mongodb.net/database-name?retryWrites=true&w=majority
SECRET_KEY=mysecretkey
```

`username`, `password`, `database-name`을 실제 MongoDB 자격 증명으로 바꿉니다.

4. 사용자 모델(`models/User.js`)을 생성합니다:

```javascript
const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const UserSchema = new Schema({
  email: { type: String, required: true, unique: true },
  password: { type: String, required: true }
});

module.exports = mongoose.model('User', UserSchema);
```

5. 5. JWT 유틸리티(`utils/jwt.js`)를 구현합니다:

```javascript
const jwt = require('jsonwebtoken');
const dotenv = require('dotenv');

dotenv.config();

function generateToken(user) {
  return jwt.sign({ id: user._id }, process.env.SECRET_KEY, { expiresIn: '24h' });
}

function verifyToken(token) {
  try {
    return jwt.verify(token, process.env.SECRET_KEY);
  } catch (err) {
    return null;
  }
}

module.exports = { generateToken, verifyToken };
```

6. 유효성 검사(`utils/validation.js`)를 구현합니다:

```javascript
function isValidEmail(email) {
  const regex = /^[\w-]+(\.[\w-]+)*@([\w-]+\.)+[a-zA-Z]{2,7}$/;
  return regex.test(email);
}

function isStrongPassword(password) {
  // At least one uppercase letter, one lowercase letter, one number and one special character, and at least 8 characters long
  const regex = /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/;
  return regex.test(password);
}

module.exports = { isValidEmail, isStrongPassword };
```

7. 사용자 등록 및 인증을 위한 경로를 생성합니다(`index.js`):

```javascript
const express = require('express');
const mongoose = require('mongoose');
const bcrypt = require('bcryptjs');
const cors = require('cors');
const bodyParser = require('body-parser');
const dotenv = require('dotenv');

const User = require('./models/User');
const { generateToken, verifyToken } = require('./utils/jwt');
const { isValidEmail, isStrongPassword } = require('./utils/validation');

dotenv.config();

mongoose.connect(process.env.MONGODB_URI, { useNewUrlParser: true, useUnifiedTopology: true, useCreateIndex: true });

const app = express();
app.use(cors());
app.use(bodyParser.json());

app.post('/register', async (req, res) => {
  const { email, password } = req.body;

  if (!isValidEmail(email)) {
    return res.status(400).json({ message: 'Invalid email format' });
  }

  if (!isStrongPassword(password)) {
    return res.status(400).json({ message: 'Weak password. Must have at least one uppercase letter, one lowercase letter, one number, one special character and be at least 8 characters long.' });
  }

  const existingUser = await User.findOne({ email });

  if (existingUser) {
    return res.status(409).json({ message: 'Email already in use' });
  }

  const hashedPassword = await bcrypt.hash(password, 10);
  const user = new User({ email, password: hashedPassword });
  await user.save();

  res.status(201).json({ message: 'User registered successfully', user });
});

app.post('/login', async (req, res) => {
  const { email, password } = req.body;

  const user = await User.findOne({ email });

  if (!user || !(await bcrypt.compare(password, user.password))) {
    return res.status(401).json({ message: 'Invalid email or password' });
  }

  const token = generateToken(user);

  res.json({ message: 'Logged in successfully', token });
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => console.log(`Server running on port ${PORT}`));
```

이제 `node index.js`를 사용하여 서버를 실행하고 Postman 또는 curl과 같은 도구로 등록 및 인증 엔드포인트를 테스트할 수 있습니다.