Access-Control-Allow-Credentials

The Access-Control-Allow-Credentials response header tells browsers whether to expose the response to 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 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, and so if a request is made for a resource with credentials, if this header is not returned with the resource, the response is ignored by the browser and not returned to 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, in order for browsers to expose the response to 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 in to including credentials.

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()