عرض عملي: مشاهدة فشل CORS وإصلاحه

خطوة بخطوة

1. Run Shop API on port 8080 and serve a small HTML page from another port (for example 3000) that calls fetch("http://localhost:8080/products").
2. Open the browser console and read the CORS error; check in the network tab that the server still answered.
3. Configure CORS for exactly http://localhost:3000 and restart.
4. Planned mistake: use allowedOrigins("*") together with credentials. Fix: list the explicit origin; the wildcard with credentials is not allowed and is unsafe.
5. Reload the page and see the call succeed; try from another origin (port 3001) and see it still fail.