Access-Control-Allow-Headers

Access-Control-Allow-Headers

The Access-Control-Allow-Headers response header is used in response to a preflight request which includes the Access-Control-Request-Headers to indicate which HTTP headers can be used during the actual request.

This header is required if the request has an Access-Control-Request-Headers header.

Syntax

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)

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. Note that the Authorization header can't be wildcarded and always needs to be listed explicitly.

Examples

A custom header

Here's an example of what an Access-Control-Allow-Headers header might look like. 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).

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

Multiple headers

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

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

Bypassing additional restrictions

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.

Access-Control-Allow-Headers: Accept

Example preflight request

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

Request

First, the request. 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).

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/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

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
Access-Control-Allow-Headers	4	12	3.5	10	12	4	2	Yes	4	12	3.2	Yes
wildcard	63	79	69	No	50	No	63	63	No	46	No	8.2

See also

• Access-Control-Allow-Origin
• Access-Control-Expose-Headers
• Access-Control-Allow-Methods
• Access-Control-Request-Headers