CORS Tutorial: Cross-Origin Resource Sharing Explained 🌐

CORS (Cross-Origin Resource Sharing) is a critical security mechanism for web applications. It allows browsers to relax the same-origin policy, enabling resources from different origins to interact safely. 🛡️

Key Concepts

• Origin: A unique combination of protocol, domain, and port (e.g., https://api.example.com:8080)
• CORS Headers:
  • Access-Control-Allow-Origin (defines permitted origins)
  • Access-Control-Allow-Methods (lists allowed HTTP methods)
  • Access-Control-Allow-Headers (specifies permitted request headers)
• Preflight Requests: OPTIONS requests sent before actual cross-origin calls to check headers

Common Use Cases

• Fetching data from a different domain (e.g., https://api.otherdomain.com/data)
• Integrating third-party APIs (e.g., Google Maps, payment gateways)
• Microservices architecture where frontends and backends reside on separate origins

Solutions & Best Practices

1. Server Configuration
   Add appropriate CORS headers to your response:

   Access-Control-Allow-Origin: https://frontend.example.com
   Access-Control-Allow-Methods: GET, POST, PUT, DELETE
   Access-Control-Allow-Headers: Content-Type, Authorization
   

2. Proxy Server
   Use a proxy to bypass CORS restrictions:

   

3. CORS Libraries
   Leverage tools like Express.js or Spring Boot for simplified implementation

Visual Guide

For deeper insights into CORS configuration, check our CORS Best Practices Guide. 📘