Node.js Backend Development Bootcamp · 课时

使用 JWT 的身份验证中间件

使用 JSON Web Token 为 Express 应用构建安全的身份验证，并学习如何通过自定义身份验证中间件保护路由。

使用 JWT 的身份验证中间件 是 CoddyKit 上的免费 Node.js Backend Development Bootcamp 课时。这是第 4 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Node.js Backend Development Bootcamp 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Node.js Backend Development Bootcamp 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Why Tokens?

HTTP is stateless: the server forgets you between requests. To know who is making a request, the client sends proof of identity each time.

JSON Web Tokens (JWT) are a popular, stateless way to carry that proof without storing sessions on the server.

Anatomy of a JWT

A JWT is three Base64 sections separated by dots:

Header: the signing algorithm
Payload: claims like user id and role
Signature: verifies the token was not tampered with

The payload is encoded, not encrypted — never put secrets in it.

// xxxxx.yyyyy.zzzzz
// header.payload.signature

Installing jsonwebtoken

The jsonwebtoken package handles creating and verifying tokens.

// npm install jsonwebtoken
const jwt = require('jsonwebtoken');

Signing a Token on Login

After verifying a user's credentials, call jwt.sign() with the payload, a secret, and options like expiry. Send the resulting token back to the client.

const token = jwt.sign(
  { userId: user.id, role: user.role },
  process.env.JWT_SECRET,
  { expiresIn: '1h' }
);
res.json({ token });

Sending the Token

The client stores the token and sends it back on each request, usually in the Authorization header using the Bearer scheme.

// Authorization: Bearer eyJhbGci...

Reading the Token in Middleware

Auth middleware extracts the token from the header. Split off the Bearer prefix to get the raw token string.

function auth(req, res, next) {
  const header = req.get('Authorization') || '';
  const token = header.split(' ')[1];
  // verify next...
}

Verifying the Token

jwt.verify() checks the signature and expiry. If valid it returns the decoded payload; if not it throws, so wrap it in try/catch.

try {
  const payload = jwt.verify(token, process.env.JWT_SECRET);
  req.user = payload;
  next();
} catch (err) {
  res.status(401).json({ error: 'Invalid token' });
}

Complete Auth Middleware

Putting it together, this middleware rejects missing or invalid tokens and attaches the user to the request for downstream handlers.

function auth(req, res, next) {
  const token = (req.get('Authorization') || '').split(' ')[1];
  if (!token) return res.status(401).json({ error: 'No token' });
  try {
    req.user = jwt.verify(token, process.env.JWT_SECRET);
    next();
  } catch {
    res.status(401).json({ error: 'Invalid token' });
  }
}

Protecting Routes

Apply the middleware to any route that requires login. Express runs it before the handler, blocking unauthenticated requests automatically.

app.get('/profile', auth, (req, res) => {
  res.json({ id: req.user.userId });
});

Role-Based Authorization

Authentication answers "who are you?"; authorization answers "are you allowed?". A second middleware can check req.user.role set by the auth step.

function requireAdmin(req, res, next) {
  if (req.user.role !== 'admin') {
    return res.status(403).json({ error: 'Forbidden' });
  }
  next();
}
app.delete('/users/:id', auth, requireAdmin, handler);

Security Best Practices

Keep tokens safe:

Store the secret in an environment variable, never in code
Use short expiry times and refresh tokens for longer sessions
Always serve over HTTPS
Return 401 for missing/invalid auth, 403 for insufficient permissions

Quick Check

Test your understanding of JWT auth.

Recap

You built stateless authentication with JWT:

Sign a token on login with jwt.sign()
Send it via the Authorization: Bearer header
Verify it in custom middleware with jwt.verify()
Attach req.user and protect routes
Add role checks for authorization

This is the foundation of secure Express APIs.

常见问题解答

「使用 JWT 的身份验证中间件」课时是免费的吗？

是的 — 「使用 JWT 的身份验证中间件」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Node.js Backend Development Bootcamp 课程的其余内容，请升级到 CoddyKit PRO。 Node.js Backend Development Bootcamp 课程共包含 4 节课。

「使用 JWT 的身份验证中间件」这节课中我会学到什么？

使用 JSON Web Token 为 Express 应用构建安全的身份验证，并学习如何通过自定义身份验证中间件保护路由。你通过在浏览器中直接运行的动手代码来练习 Node.js Backend Development Bootcamp，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Node.js Backend Development Bootcamp 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Node.js Backend Development Bootcamp 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 4 节课，共 4 节。

「使用 JWT 的身份验证中间件」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Node.js Backend Development Bootcamp 课中编写并运行代码吗？

能。每节 Node.js Backend Development Bootcamp 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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