CORS (Cross-Origin Resource Sharing) is a security feature implemented in web browsers that restricts web pages or web applications from making requests to a different domain than the one the page originated from. This security measure is in place to prevent malicious scripts from accessing sensitive data or performing unwanted actions on behalf of the user.
When a web page or application attempts to make a cross-origin request, the browser sends a preflight request to the server to check whether the request is allowed. The server then responds with the necessary headers to indicate whether the request is permitted or not. If the request is allowed, the browser sends the actual request to the server, and the server responds with the requested data.
CORS is implemented using HTTP headers, which allow the server to control which domains are allowed to make requests, and what types of requests are allowed. The two primary headers used in CORS are:
Access-Control-Allow-Origin: This header indicates which domain(s) are allowed to make cross-origin requests to the server. The value can be a specific domain, "*", which allows any domain to make requests, or null, which means that no domains are allowed to make requests.
Access-Control-Allow-Methods: This header indicates which HTTP methods (GET, POST, PUT, DELETE, etc.) are allowed for cross-origin requests.
Other headers may also be used to provide additional information or control over cross-origin requests.
Overall, CORS is an important security feature that helps prevent malicious scripts from accessing sensitive data or performing unwanted actions on behalf of the user. It allows servers to control which domains are allowed to make requests and what types of requests are permitted, ensuring that sensitive data and actions remain secure.