What is the purpose of the OPTIONS method? When is it sent automatically?

The HTTP OPTIONS method is used to request information from the server about the supported methods and capabilities of a resource. It allows the client to find out which HTTP methods (GET, POST, PUT, DELETE, etc.) are permitted for a specific URL.

An OPTIONS request is automatically sent by the browser as part of the CORS (Cross-Origin Resource Sharing) mechanism as a "preflight" request before the main request if:

• It uses methods other than simple ones (GET, POST, HEAD), such as PUT or DELETE.
• It uses non-standard headers.
• It sends data with a type other than simple (e.g., application/json).

This is done to check whether the server allows such a request from the current origin, to ensure security.

Example: When sending an AJAX request with the PUT method to another domain, the browser will first send an OPTIONS request to get permissions, and only after a successful response will it perform the main request.