From f199b7a7ede5f0975d65f28e16dade163a830e92 Mon Sep 17 00:00:00 2001
From: Arnas Donauskas <arnas.donauskas@hostinger.com>
Date: Mon, 20 Apr 2026 19:24:41 +0300
Subject: [PATCH] security: baseline response headers (CSP report-only + OWASP
 set)
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Adds a catch-all rule in next.config.ts that merges a set of baseline
security headers into every response — served alongside the existing
Cache-Control rules, not instead of them.

Enforced today:
  - Strict-Transport-Security: 2yr, includeSubDomains, preload-eligible.
    No-op on http://localhost.
  - X-Content-Type-Options: nosniff
  - X-Frame-Options: DENY  (same defense as frame-ancestors below, but
    older browsers only read this one)
  - Referrer-Policy: strict-origin-when-cross-origin
  - Permissions-Policy: deny camera/mic/geolocation/payment/usb. We
    don't use any of those APIs; closing them off prevents a supply-
    chain compromise or a forgotten plugin from silently enabling them.

Report-only:
  - Content-Security-Policy-Report-Only with a pragmatic allowlist:
      default-src 'self'
      script-src  'self' 'unsafe-inline' 'unsafe-eval'
      style-src   'self' 'unsafe-inline'
      img-src     'self' data: blob: https:
      font-src    'self' data:
      connect-src 'self' https://*.supabase.co wss://*.supabase.co
      frame-ancestors 'none'
      base-uri    'self'
      form-action 'self'
    'unsafe-inline' / 'unsafe-eval' are there because Next's inline
    hydration script + dev-mode require them; nonce-based CSP is a
    later project. Violations appear in the browser console but
    nothing is blocked until we flip the header name to
    `Content-Security-Policy`.

Verified against the running dev server:
  - /, /docs, /login, /api/whatsapp/webhook, /_next/static/* all
    return the six headers.
  - No CSP violations on / or /docs in the browser console.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 next.config.ts | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/next.config.ts b/next.config.ts
index 72f70b9..02bd16f 100644
--- a/next.config.ts
+++ b/next.config.ts
@@ -1,5 +1,58 @@
 import type { NextConfig } from "next";
 
+/**
+ * Baseline security headers applied to every response.
+ *
+ * CSP ships as `Content-Security-Policy-Report-Only` so the browser
+ * surfaces violations in the console without blocking anything — once
+ * we have confidence nothing legit trips it (two deploys, a pass on
+ * every route), flip the key to `Content-Security-Policy` to enforce.
+ *
+ * The rest of the headers are straight blocks, safe to enforce today:
+ *   - HSTS: only meaningful on HTTPS (no-op on http://localhost).
+ *   - X-Content-Type-Options / X-Frame-Options / Referrer-Policy:
+ *     baseline OWASP hardening, no behavioural cost.
+ *   - Permissions-Policy: we don't use camera / microphone / etc, so
+ *     deny them. A supply-chain compromise or a forgotten plugin
+ *     can't silently opt back in.
+ */
+const SECURITY_HEADERS = [
+  {
+    key: "Strict-Transport-Security",
+    value: "max-age=63072000; includeSubDomains; preload",
+  },
+  { key: "X-Content-Type-Options", value: "nosniff" },
+  { key: "X-Frame-Options", value: "DENY" },
+  { key: "Referrer-Policy", value: "strict-origin-when-cross-origin" },
+  {
+    key: "Permissions-Policy",
+    value: "camera=(), microphone=(), geolocation=(), payment=(), usb=()",
+  },
+  {
+    key: "Content-Security-Policy-Report-Only",
+    value: [
+      "default-src 'self'",
+      // Next.js needs 'unsafe-inline' for its inline hydration script
+      // and 'unsafe-eval' in dev + some production optimisations.
+      // Nonce-based CSP is a later project.
+      "script-src 'self' 'unsafe-inline' 'unsafe-eval'",
+      // Tailwind + inline style attributes on lots of components.
+      "style-src 'self' 'unsafe-inline'",
+      // Supabase public-bucket avatars, contact avatars (arbitrary
+      // https URLs paste-able from the UI), OG images, data URLs for
+      // tiny inline assets.
+      "img-src 'self' data: blob: https:",
+      "font-src 'self' data:",
+      // Supabase REST + realtime (WSS). All Meta API calls happen
+      // server-side, so graph.facebook.com does not belong here.
+      "connect-src 'self' https://*.supabase.co wss://*.supabase.co",
+      "frame-ancestors 'none'",
+      "base-uri 'self'",
+      "form-action 'self'",
+    ].join("; "),
+  },
+] as const;
+
 const nextConfig: NextConfig = {
   /**
    * Cache-Control policy.
@@ -32,6 +85,11 @@ const nextConfig: NextConfig = {
    *   from a shared cache. The s-maxage here is a ceiling; Next.js
    *   and auth middleware still set `private` / `no-store` for
    *   per-user responses.
+   *
+   * Security headers are appended via a separate catch-all rule
+   * below — Next.js merges headers from every matching rule, so
+   * they apply to every response regardless of which cache rule
+   * matched.
    */
   async headers() {
     return [
@@ -58,6 +116,13 @@ const nextConfig: NextConfig = {
           },
         ],
       },
+      {
+        // Security headers on every response, including /_next/static
+        // assets (nosniff matters there) and /api/* (HSTS + referrer-
+        // policy don't hurt).
+        source: "/:path*",
+        headers: [...SECURITY_HEADERS],
+      },
     ];
   },
 };