index.md

---

title: Access-Control-Allow-Headers
slug: Web/HTTP/Headers/Access-Control-Allow-Headers
browser-compat: http.headers.Access-Control-Allow-Headers

---

{{HTTPSidebar}}

The Access-Control-Allow-Headers response header is used in response to a {{glossary("preflight request")}} which includes the {{HTTPHeader("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 {{HTTPHeader("Access-Control-Request-Headers")}} header.

Note: {{glossary("CORS-safelisted_request_header", "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 safelist additional restrictions).

Header type	{{Glossary("Response header")}}
{{Glossary("Forbidden header name")}}	no

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 {{HTTPHeader("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 {{glossary("CORS-safelisted_request_header", "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 {{glossary("CORS-safelisted_request_header", "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 {{glossary("preflight request")}} involving Access-Control-Allow-Headers.

Request

First, the request. The preflight request is an {{HTTPMethod("OPTIONS")}} request that includes some combination of the three preflight request headers: {{HTTPHeader("Access-Control-Request-Method")}}, {{HTTPHeader("Access-Control-Request-Headers")}}, and {{HTTPHeader("Origin")}}.

The preflight request below tells the server that we want to send a CORS GET request with the headers listed in {{HTTPHeader("Access-Control-Request-Headers")}} ({{HTTPHeader("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 {{HTTPHeader("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

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{HTTPHeader("Access-Control-Allow-Origin")}}

• {{HTTPHeader("Access-Control-Expose-Headers")}}

• {{HTTPHeader("Access-Control-Allow-Methods")}}

• {{HTTPHeader("Access-Control-Request-Headers")}}