CORS
Cross-Origin Resource Sharing
A browser security mechanism that controls which domains can access resources from another domain.
Technical Detail
CORS is enforced by browsers, not servers. The preflight OPTIONS request checks Access-Control-Allow-Origin, Access-Control-Allow-Methods, and Access-Control-Allow-Headers. Responses must include these headers for cross-origin requests to succeed. 'Access-Control-Allow-Origin: *' allows any domain but blocks credentials (cookies). For credentialed requests, the exact origin must be specified. CORS only protects browsers — server-to-server requests bypass CORS entirely.
Example
```javascript
// CORS: web API example
const response = await fetch('/api/resource');
const data = await response.json();
console.log(data);
```
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