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How does CORS restrict or allow cross-origin API requests?

Asked on Nov 11, 2025

Answer

CORS (Cross-Origin Resource Sharing) is a security feature implemented by web browsers to control how resources are shared between different origins. It allows servers to specify who can access their resources and which HTTP methods are permitted when accessing them from a different origin.

Example Concept: CORS uses HTTP headers to determine whether a browser should block or allow a cross-origin request. The server responds with headers like "Access-Control-Allow-Origin" to specify which origins are permitted. If the origin of the request matches the allowed origins, the browser allows the request; otherwise, it blocks it. This mechanism helps prevent malicious websites from accessing sensitive data from another domain.

Additional Comment:

CORS is enforced by browsers, not by servers.
Preflight requests are used for HTTP methods other than GET or POST, or when custom headers are involved.
Servers can specify allowed methods and headers using "Access-Control-Allow-Methods" and "Access-Control-Allow-Headers".
For credentials, the "Access-Control-Allow-Credentials" header must be set to true, and the "Access-Control-Allow-Origin" cannot be a wildcard.

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Ask any question about Web Development here... and get an instant response.

How does CORS restrict or allow cross-origin API requests?

Asked on Nov 11, 2025

Answer

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