CORS (Cross-Origin Resource Sharing) is one of the most frustrating challenges developers face when working with REST APIs. You make a request, and suddenly, the browser blocks it with the dreaded "No ‘Access-Control-Allow-Origin’ header" error. But why does this happen, and how do you fix it without compromising security? In this video, we’ll break down how CORS works, why the Same-Origin Policy exists, and the difference between Simple Requests and Preflight Requests. We’ll dive into real-world solutions, from backend fixes using and Spring Boot to frontend workarounds like proxies and browser extensions. If you’ve ever struggled with cross-origin issues, this is your ultimate guide to fixing CORS the right way. 📌 Timestamps 🔹 00:00 – Introduction to CORS & Why It Matters 🔹 00:20 – What is Cross-Origin Resource Sharing (CORS)? 🔹 00:49 – How Browsers Enforce CORS & Why Requests Get Blocked 🔹 02:00 – CORS Headers Explained: Access-Control-Allow-Origin & More 🔹 03:15 – Preflight Requests & How OPTIONS Method Works 🔹 04:11 – Fixing CORS Errors in Backend & Frontend 🔹 04:48 – Best Practices for Secure CORS Implementation AWS Certification: AWS Certified Cloud Practioner: AWS Certified Solution Architect Associate: AWS Certified Solution Architect Professional: #CORS #RESTAPI #WebSecurity