CORS

Browsers enforce the same-origin policy to prevent malicious cross-site requests. Preflight acts as a “handshake” before sensitive requests, asking: “Server, are you cool with this?” 🔥 Triggers for Preflight: Non-simple HTTP methods (PUT, DELETE, PATCH) Custom headers (e.g., X-API-Token) “Advanced” Content-Types (e.g., application/json) Credentialed requests (with cookies/auth) ✅ Simple requests (GET/POST with basic headers) skip preflight! 🔁 How Preflight Works: A 2-Step Dance sequenceDiagram Browser->>Server: OPTIONS Request (Preflight) Note left of Browser: Headers sent:<br>📍 Origin<br>📍 Access-Control-Request-Method<br>📍 Access-Control-Request-Headers alt Server Allows Server-->>Browser: 200 OK + CORS Headers Note right of Server: Headers returned:<br>✅ Access-Control-Allow-Origin<br>✅ Access-Control-Allow-Methods<br>✅ Access-Control-Allow-Headers Browser->>Server: Actual Request (e.g., DELETE) else Server Denies Server-->>Browser: CORS Error Blocked! end ⚙️ Server-Side Setup Essentials Handle OPTIONS requests correctly: ...

Understanding Cross-Origin Resource Sharing (CORS): A Beginner’s Guide In the world of web development, security is paramount. One crucial aspect of securing web applications is understanding how to manage Cross-Origin Resource Sharing, commonly known as CORS. This concept can be a bit daunting for beginners, so in this blog post, we’ll break down CORS in a way that’s easy to understand and implement. What is CORS? CORS is a security feature implemented by web browsers to prevent malicious websites from accessing resources from another domain without permission. Essentially, it allows web servers to define who can access their resources and how. It’s a policy used to relax the same-origin policy, which is a security measure that restricts how a document or script from one origin can interact with resources from another origin. ...