Access-Control-Allow-Credentials header

The HTTP Access-Control-Allow-Credentials {{Glossary("response header")}} tells browsers whether the server allows credentials to be included in cross-origin HTTP requests.

Credentials include cookies, {{glossary("TLS", "Transport Layer Security (TLS)")}} client certificates, or authentication headers containing a username and password. By default, these credentials are not sent in cross-origin requests, and doing so can make a site vulnerable to {{Glossary("CSRF", "Cross-Site Request Forgery (CSRF)")}} attacks.

A client can ask for credentials to be included in cross-site requests in several ways:

• Using {{domxref("Window/fetch", "fetch()")}}, by setting the credentials option to "include".
• Using {{domxref("XMLHttpRequest")}}, by setting the {{domxref("XMLHttpRequest.withCredentials")}} property to true.
• Using {{domxref("EventSource()")}}, by setting the {{domxref("EventSource.withCredentials")}} property to true.

When credentials are included:

• For {{glossary("Preflight_request", "preflighted")}} requests: The preflight request does not include credentials. If the server's response to the preflight request sets the Access-Control-Allow-Credentials header to true, then the real request will include credentials; otherwise, the browser reports a network error.
• For non-preflighted requests: The request will include credentials, and if the server's response does not set the Access-Control-Allow-Credentials header to true, the browser reports a network error.

Syntax

Access-Control-Allow-Credentials: true

Directives

• true
  • : The server allows credentials to be included in cross-origin HTTP requests. This is the only valid value for this header and is case-sensitive. If you don't need credentials, omit this header entirely rather than setting its value to false.

Examples

Allow credentials:

Access-Control-Allow-Credentials: true

Using {{domxref("Window/fetch", "fetch()")}} with credentials:

fetch(url, {
  credentials: "include",
});

Using {{domxref("XMLHttpRequest")}} with credentials:

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

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{domxref("XMLHttpRequest.withCredentials")}}
• {{domxref("Request.Request()", "Request()")}}