Then the browser will permit the requesting website to read the response, because the Access-Control-Allow-Credentials response header is set to true. Now if the requesting website uses JavaScript to declare that it is sending cookies with the request: However, the cross-domain server can permit reading of the response when credentials are passed to it by setting the CORS Access-Control-Allow-Credentials header to true. The default behavior of cross-origin resource requests is for requests to be passed without credentials like cookies and the Authorization header. Handling cross-origin resource requests with credentials However, no browser supports multiple origins and there are restrictions on the use of the wildcard *. The specification of Access-Control-Allow-Origin allows for multiple origins, or the value null, or the wildcard *. The browser will allow code running on to access the response because the origins match. The server on returns the following response: This header is returned by a server when a website requests a cross-domain resource, with an Origin header added by the browser.įor example, suppose a website with origin causes the following cross-domain request: The CORS specification identifies a collection of protocol headers of which Access-Control-Allow-Origin is the most significant. The cross-origin resource sharing (CORS) specification prescribes header content exchanged between web servers and browsers that restricts origins for web resource requests outside of the origin domain. Implementing simple cross-origin resource sharing A web browser compares the Access-Control-Allow-Origin with the requesting website's origin and permits access to the response if they match. The Access-Control-Allow-Origin header is included in the response from one website to a request originating from another website, and identifies the permitted origin of the request. What is the Access-Control-Allow-Origin response header? Browsers permit access to responses to cross-origin requests based upon these header instructions. The cross-origin resource sharing specification provides controlled relaxation of the same-origin policy for HTTP requests to one website domain from another through the use of a collection of HTTP headers. In this section we explain what the Access-Control-Allow-Origin header is in respect of CORS, and how it forms part of CORS implementation. CORS and the Access-Control-Allow-Origin response header
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