CORS Deep Dive

Understand Cross-Origin Resource Sharing from the ground up. Learn why browsers enforce CORS, how preflight requests work, and how to configure CORS correctly for your API.

Usage

Ask about CORS configuration, debugging CORS errors, or understanding the security implications of CORS settings.

Examples

• "Why am I getting a CORS error and how do I fix it?"
• "How do I configure CORS for an API that uses cookies?"
• "What is a preflight request and when does it happen?"

Guidelines

• Never use Access-Control-Allow-Origin: * with credentials
• Understand the difference between simple and preflighted requests
• Whitelist specific origins instead of reflecting the Origin header blindly
• Cache preflight responses with Access-Control-Max-Age to reduce latency
• CORS is enforced by browsers only — it does not protect your API from non-browser clients