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Introduction: What Is CORS and Why It Matters
Cross-Origin Resource Sharing (CORS) is a browser security mechanism that controls how web applications allow resources to be requested from domains other than their own.
By default, browsers enforce the Same-Origin Policy (SOP), which prevents a website from reading responses from another domain. This is a foundational security control that protects users from malicious websites stealing sensitive data from authenticated sessions.
CORS exists to safely relax this restriction when cross-origin access is legitimately required — for example, when a frontend application hosted on one domain needs to communicate with an API hosted on another.
CORS behavior is enforced entirely through HTTP response headers, most notably:
Access-Control-Allow-OriginAccess-Control-Allow-CredentialsAccess-Control-Allow-MethodsAccess-Control-Allow-Headers
When implemented correctly, CORS enables secure cross-domain communication.
When misconfigured, however, it can turn a user’s browser into a data exfiltration…