JWT Authentication Middleware

const jwt = require('jsonwebtoken');

const requireAuth = (req, res, next) => {
  // 1. Check if the Authorization header exists
  const authHeader = req.headers.authorization;
  if (!authHeader || !authHeader.startsWith('Bearer ')) {
    return res.status(401).json({ error: 'Unauthorized: No token provided' });
  }

  // 2. Extract the token (Remove "Bearer ")
  const token = authHeader.split(' ')[1];

  try {
    // 3. Verify the token using the secret key
    // If it's expired or tampered with, this will throw an error
    const decodedPayload = jwt.verify(token, process.env.JWT_SECRET);

    // 4. Attach the decoded payload to the request object
    req.user = decodedPayload;

    // 5. Move to the next middleware/route handler
    next();
  } catch (err) {
    return res.status(403).json({ error: 'Forbidden: Invalid or expired token' });
  }
};

module.exports = requireAuth;

const express = require('express');
const requireAuth = require('./middleware/auth');
const app = express();

// Public route (No token needed)
app.get('/public', (req, res) => res.send("Anyone can see this"));

// Protected route (Token required)
app.get('/dashboard', requireAuth, (req, res) => {
  // Because requireAuth ran successfully, we know req.user exists!
  res.send(`Welcome to your dashboard, user ID: ${req.user.userId}`);
});

// Protect an entire group of routes:
app.use('/api/secure', requireAuth);
app.get('/api/secure/data', (req, res) => res.send("Secure data"));