fix(codespaces): allow Server Actions from forwarded hosts

README.md

@@ -221,3 +221,15 @@ I'm the developer behind Developers Digest. If you find my work helpful or enjoy
 - **Website**: Check out my website at [developersdigest.tech](https://developersdigest.tech)
 - **Github**: Follow me on GitHub at [github.com/developersdigest](https://github.com/developersdigest)
 - **Twitter**: Follow me on Twitter at [twitter.com/dev__digest](https://twitter.com/dev__digest)
+
+## Troubleshooting
+
+### GitHub Codespaces: "x-forwarded-host" does not match "origin"
+
+If you run this in GitHub Codespaces you may see:
+
+- `x-forwarded-host header ... does not match origin header ...`
+- `Error: Invalid Server Actions request.`
+
+This is caused by Next.js Server Actions CSRF protection when the app is behind a proxy.
+This repo includes a `next.config.mjs` that allows Codespaces forwarded hosts.

next.config.mjs

@@ -0,0 +1,26 @@
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  // Fix for GitHub Codespaces (and other proxy setups) where Server Actions
+  // requests may arrive with forwarded hosts that don't match the `origin`
+  // header. Next.js blocks these by default for CSRF protection.
+  //
+  // Next.js 14.1.x expects this under `experimental.serverActions`.
+  // See: https://nextjs.org/docs/app/api-reference/config/next-config-js/serverActions#allowedorigins
+  experimental: {
+    serverActions: {
+      allowedOrigins: [
+        // local dev
+        'localhost',
+        '127.0.0.1',
+
+        // GitHub Codespaces
+        '*.app.github.dev',
+
+        // Vercel preview/prod (VERCEL_URL is e.g. "my-app.vercel.app")
+        ...(process.env.VERCEL_URL ? [process.env.VERCEL_URL] : []),
+      ],
+    },
+  },
+};
+
+export default nextConfig;