What is CORS and what does it mean?

CORS (Cross-Origin Resource Sharing) is a browser security mechanism that restricts web pages from making requests to resources on a different domain (origin).

By default, browsers block such cross-origin requests due to the Same-Origin Policy to prevent attacks like XSS and CSRF.

CORS allows the server to explicitly specify which domains can access its resources through special HTTP headers, such as:

• Access-Control-Allow-Origin — specifies which sources are permitted.
• Access-Control-Allow-Methods — specifies which HTTP methods are allowed.
• Access-Control-Allow-Headers — specifies which headers are allowed.

If the browser sees that the server permits a request from the current domain, it allows the request to proceed. Otherwise, it blocks it.

Thus, CORS is a way to control access to server resources from the browser, balancing security and functionality of web applications.