Introduction to JSON Web Tokens (JWT)

JSON Web Tokens (JWT) are an open standard (RFC 7519) that define a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with the HMAC algorithm) or a public/private key pair using RSA or ECDSA. This article explores the jsonwebtoken library in Node.js, offering a thorough introduction to its functionalities and practical examples of usage.

Installation

npm install jsonwebtoken

APIs and Usage

1. Creating a Token

To create a token, you need to sign it with a secret or a private key. Here’s how to do it:

const jwt = require('jsonwebtoken');

const payload = {
    id: '123abc',
    role: 'admin'
};

const secret = 'mySecretKey';

const token = jwt.sign(payload, secret, { expiresIn: '1h' });

console.log('Generated Token:', token);

2. Verifying a Token

Verifying a token ensures its integrity and authenticity. Here’s an example:

jwt.verify(token, secret, (err, decoded) => {
    if (err) {
        console.error('Token verification failed:', err);
    } else {
        console.log('Decoded Payload:', decoded);
    }
});

3. Decoding a Token Without Verification

To get the payload of a token without verifying it, use jwt.decode():

const decoded = jwt.decode(token);
console.log('Decoded Payload without verification:', decoded);

4. Asynchronous and Synchronous Signing and Verification

In addition to asynchronously signing and verifying tokens, you can do so synchronously:

// Synchronous signing
const token = jwt.sign(payload, secret, { expiresIn: '1h' });
console.log('Generated Token:', token);

// Synchronous verifying
try {
    const decoded = jwt.verify(token, secret);
    console.log('Decoded Payload:', decoded);
} catch (err) {
    console.error('Token verification failed:', err);
}

Sample Application

Below is an example of a basic Express application implementing JWT for securing routes:

const express = require('express');
const jwt = require('jsonwebtoken');

const app = express();
const secret = 'mySecretKey';

app.use(express.json());

// Middleware to protect routes
function authenticateToken(req, res, next) {
    const token = req.headers['authorization'];
    if (!token) return res.sendStatus(401);

    jwt.verify(token, secret, (err, user) => {
        if (err) return res.sendStatus(403);
        req.user = user;
        next();
    });
}

app.post('/login', (req, res) => {
    // Assume user is authenticated and get user info
    const user = { id: req.body.id, role: req.body.role };
    const token = jwt.sign(user, secret, { expiresIn: '1h' });
    res.json({ token });
});

app.get('/protected', authenticateToken, (req, res) => {
    res.json({ message: 'This is a protected route', user: req.user });
});

app.listen(3000, () => {
    console.log('Server started on port 3000');
});

With this foundational knowledge, you can further explore JWTs to strengthen security in your applications.

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