Access-Control-Allow-Headers

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

* Some parts of this feature may have varying levels of support.

The HTTP Access-Control-Allow-Headersresponse header is used in response to a preflight request to indicate the HTTP headers that can be used during the actual request. This header is required if the preflight request contains Access-Control-Request-Headers.

Note: The CORS-safelisted request headers are always allowed and usually aren't listed in Access-Control-Allow-Headers unless there is a need to circumvent the additional safelist restrictions.

Header typeResponse header
Forbidden request headerNo

Syntax

http
Access-Control-Allow-Headers: <header-name> Access-Control-Allow-Headers: <header-name>, <header-name> Access-Control-Allow-Headers: *

Directives

<header-name>

The name of a supported request header. The header may list any number of headers, separated by commas.

* (wildcard)

Any header. The value * only counts as a special wildcard value for requests without credentials (requests without HTTP cookies or HTTP authentication information). In requests with credentials, it is treated as the literal header name * without special semantics. The Authorization header can't be wildcarded and always needs to be listed explicitly.

Examples

Implementing a custom header

Below is an example of an Access-Control-Allow-Headers header. It indicates that a custom header named X-Custom-Header is supported by CORS requests to the server, in addition to the CORS-safelisted request headers.

http
Access-Control-Allow-Headers: X-Custom-Header

Supporting multiple headers

This example shows Access-Control-Allow-Headers when it specifies support for multiple headers.

http
Access-Control-Allow-Headers: X-Custom-Header, Upgrade-Insecure-Requests

Bypassing additional restrictions on CORS-safelisted headers

Although CORS-safelisted request headers are always allowed and don't usually need to be listed in Access-Control-Allow-Headers, listing them anyway will circumvent the additional restrictions that apply.

http
Access-Control-Allow-Headers: Accept

Handling preflight requests

Let's look at an example of a preflight request involving Access-Control-Allow-Headers.

Request

First, the preflight request is an OPTIONS request that includes some combination of the three preflight request headers: Access-Control-Request-Method, Access-Control-Request-Headers, and Origin.

The preflight request below tells the server that we want to send a CORS GET request with the headers listed in Access-Control-Request-Headers (Content-Type and X-Requested-With).

http
OPTIONS /resource/foo Access-Control-Request-Method: GET Access-Control-Request-Headers: content-type,x-requested-with Origin: https://foo.bar.org

Response

If the CORS request indicated by the preflight request is authorized, the server will respond to the preflight request with a message that indicates the allowed origin, methods, and headers. Below, we see that Access-Control-Allow-Headers includes the headers that were requested.

http
HTTP/1.1 200 OK Content-Length: 0 Connection: keep-alive Access-Control-Allow-Origin: https://foo.bar.org Access-Control-Allow-Methods: POST, GET, OPTIONS, DELETE Access-Control-Allow-Headers: Content-Type, x-requested-with Access-Control-Max-Age: 86400

If the requested method isn't supported, the server will respond with an error.

Specifications

Specification
Fetch
# http-access-control-allow-headers

Browser compatibility

See also