BillTracker/middleware/securityHeaders.js

'use strict';

const crypto = require('crypto');

/**
 * Generates a secure nonce for CSP policy.
 * Call once per request to get a unique nonce.
 */
function getCspNonce(req) {
  if (!req.cspNonce) {
    req.cspNonce = crypto.randomBytes(16).toString('base64');
  }
  return req.cspNonce;
}

/**
 * Applies baseline security response headers on every request.
 * 
 * Content Security Policy (CSP) is now implemented with nonce-based policies
 * to support Tailwind/shadcn inline styles and Vite build hashes.
 */
function securityHeaders(req, res, next) {
  // CSP Header - nonce-based policy for Tailwind and Vite
  const nonce = getCspNonce(req);
  const cspPolicy = 
    `default-src 'self'; ` +
    `script-src 'self' 'nonce-${nonce}'; ` +
    `style-src 'self' 'unsafe-inline' 'nonce-${nonce}'; ` +
    `img-src 'self' data:; ` +
    `font-src 'self'; ` +
    `connect-src 'self'; ` +
    `frame-ancestors 'self'; ` +
    `form-action 'self'; ` +
    `base-uri 'self'; ` +
    `object-src 'none';`;
  
  res.setHeader('Content-Security-Policy', cspPolicy);

  // Prevent MIME-type sniffing (browsers must respect Content-Type)
  res.setHeader('X-Content-Type-Options', 'nosniff');

  // Disallow embedding in iframes from other origins — prevents clickjacking
  res.setHeader('X-Frame-Options', 'SAMEORIGIN');

  // Don't send full URL in Referer header to third-party origins
  res.setHeader('Referrer-Policy', 'strict-origin-when-cross-origin');

  // Disallow cross-domain policy files (Flash/PDF legacy attack surface)
  res.setHeader('X-Permitted-Cross-Domain-Policies', 'none');

  // Don't advertise the server tech stack
  res.removeHeader('X-Powered-By');

  // HSTS — only set when the app is explicitly configured to run over HTTPS.
  // Setting this on HTTP breaks the site. Enable with HTTPS=true env var.
  if (process.env.HTTPS === 'true') {
    res.setHeader('Strict-Transport-Security', 'max-age=31536000; includeSubDomains');
  }

  next();
}

module.exports = { securityHeaders, getCspNonce };