What is CORS (Cross-Origin Resource Sharing)?
Cross-Origin Resource Sharing
CORS, or Cross-Origin Resource Sharing, is a security feature in web development that allows or restricts web applications from making requests to a different domain than the one that served the web page. It helps prevent malicious sites from accessing sensitive data from another site without permission.
Overview
Cross-Origin Resource Sharing (CORS) is a mechanism that uses HTTP headers to tell browsers to give web applications permission to access resources from a different origin. An origin is defined by the combination of the protocol, domain, and port number. For example, a web page served from 'https://example.com' cannot normally request resources from 'https://anotherdomain.com' unless the latter explicitly allows it through CORS headers. When a web application attempts to make a request to a different origin, the browser sends a preflight request to check if the actual request is safe to send. This preflight request uses the OPTIONS method and includes headers that indicate the intended method and headers of the actual request. If the server responds with the appropriate CORS headers, the browser will then proceed with the actual request; otherwise, it will block the request. CORS is important because it protects users' data and prevents unauthorized access to resources. For instance, if a user is logged into their bank account, a malicious site should not be able to access that information. By implementing CORS, developers can ensure that only trusted domains can interact with their resources, enhancing security in web applications.