Access-Control-Allow-Credentials

The Access-Control-Allow-Credentials response header tells browsers whether to expose the response to the frontend JavaScript code when the request's credentials mode (Request.credentials) is include.

When a request's credentials mode (Request.credentials) is include, browsers will only expose the response to the frontend JavaScript code if the Access-Control-Allow-Credentials value is true.

Credentials are cookies, authorization headers, or TLS client certificates.

When used as part of a response to a preflight request, this indicates whether or not the actual request can be made using credentials. Note that simple GET requests are not preflighted. So, if a request is made for a resource with credentials, and if this header is not returned with the resource; the response is ignored by the browser and not returned to the web content.

The Access-Control-Allow-Credentials header works in conjunction with the XMLHttpRequest.withCredentials property or with the credentials option in the Request() constructor of the Fetch API. For a CORS request with credentials, for browsers to expose the response to the frontend JavaScript code, both the server (using the Access-Control-Allow-Credentials header) and the client (by setting the credentials mode for the XHR, Fetch, or Ajax request) must indicate that they’re opting into including credentials.

Access-Control-Allow-Credentials: true

true

The only valid value for this header is true (case-sensitive). If you don't need credentials, omit this header entirely (rather than setting its value to false).

Allow credentials:

Access-Control-Allow-Credentials: true

Using XHR with credentials:

var xhr = new XMLHttpRequest();
xhr.open('GET', 'http://example.com/', true);
xhr.withCredentials = true;
xhr.send(null);

Using Fetch with credentials:

fetch(url, {
  credentials: 'include'
})

• XMLHttpRequest.withCredentials
• Request()