Implementing CSRF Protection in Node.js Express Applications

const express = require('express');
const cookieParser = require('cookie-parser');
const session = require('express-session');
const csurf = require('csurf');

const app = express();

// Basic setup for session and cookie-parser
app.use(cookieParser());
app.use(session({
  secret: 'your_super_secret_key',
  resave: false,
  saveUninitialized: true,
  cookie: { secure: process.env.NODE_ENV === 'production', httpOnly: true, sameSite: 'lax' }
}));

// CSRF protection middleware
const csrfProtection = csurf({ cookie: true });

// Middleware to parse incoming request bodies
app.use(express.urlencoded({ extended: false })); // For form submissions
app.use(express.json()); // For JSON payloads

// Example route requiring CSRF protection for POST requests
app.get('/form', csrfProtection, (req, res) => {
  res.send(`
    <form action="/process" method="POST">
      <input type="hidden" name="_csrf" value="${req.csrfToken()}">
      <input type="text" name="data">
      <button type="submit">Submit</button>
    </form>
  `);
});

app.post('/process', csrfProtection, (req, res) => {
  // If we reach here, CSRF token is valid
  res.send(`Data received: ${req.body.data} (CSRF protected!)`);
});

// Error handler for CSRF issues
app.use((err, req, res, next) => {
  if (err.code === 'EBADCSRFTOKEN') {
    res.status(403).send('Invalid CSRF token.');
  } else {
    next(err);
  }
});

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