The Cross-Origin Resource Sharing standard works by adding new HTTP headers that let servers describe which origins are permitted to read that information from a web browser. Modern browsers use CORS in APIs such as XMLHttpRequest or Fetch to mitigate the risks of cross-origin HTTP requests. The CORS mechanism supports secure cross-origin requests and data transfers between browsers and servers.

This means that a web application using those APIs can only request resources from the same origin the application was loaded from unless the response from other origins includes the right CORS headers. For example, XMLHttpRequest and the Fetch API follow the same-origin policy. įor security reasons, browsers restrict cross-origin HTTP requests initiated from scripts. In that preflight, the browser sends headers that indicate the HTTP method and headers that will be used in the actual request.Īn example of a cross-origin request: the front-end JavaScript code served from uses XMLHttpRequest to make a request for.

CORS also relies on a mechanism by which browsers make a 'preflight' request to the server hosting the cross-origin resource, in order to check that the server will permit the actual request. Cross-Origin Resource Sharing ( CORS) is an HTTP-header based mechanism that allows a server to indicate any origins (domain, scheme, or port) other than its own from which a browser should permit loading resources.

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