fix(preview): Ensure the protocol in redirects from server actions

Author: sommeeeer

packages/cloudflare/src/cli/templates/init.ts

@@ -132,6 +132,14 @@ function populateProcessEnv(url: URL, env: CloudflareEnv) {
       port: url.port,
     },
   });
+
+  /* We need to set this environment variable to make redirects work properly in preview mode.
+   * Next sets this in standalone mode during `startServer`. Without this the protocol would always be `https` here:
+   * https://github.com/vercel/next.js/blob/6b1e48080e896e0d44a05fe009cb79d2d3f91774/packages/next/src/server/app-render/action-handler.ts#L307-L316
+   */
+  if (url.hostname === "localhost") {
+    process.env.__NEXT_PRIVATE_ORIGIN = url.origin;
+  }
 }
 
 /* eslint-disable no-var */