cors

CORS is a browser-enforced security protocol that uses HTTP headers to grant web applications permission to access resources from different origins.

Modern browsers implement Cross-Origin Resource Sharing (CORS) to relax the Same-Origin Policy (SOP) under controlled conditions. When a script at domain-a.com requests data from domain-b.com, the browser executes a preflight check using the OPTIONS method. The server must respond with specific headers (like Access-Control-Allow-Origin: https://domain-a.com) to authorize the transaction. This mechanism prevents malicious sites from hijacking sensitive data while enabling essential integrations like RESTful APIs, cloud storage buckets, and third-party fonts.

https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS