Access-Control-Request-Headers header

The HTTP Access-Control-Request-Headers {{Glossary("request header")}} is used by browsers when issuing a {{glossary("preflight request")}} to let the server know which HTTP headers the client might send when the actual request is made (such as with {{domxref("Window/fetch", "fetch()")}} or {{domxref("XMLHttpRequest.setRequestHeader()")}}). The complementary server-side header of {{HTTPHeader("Access-Control-Allow-Headers")}} will answer this browser-side header.

Header type	{{Glossary("Request header")}}
{{Glossary("Forbidden request header")}}	Yes

Syntax

Access-Control-Request-Headers: <header-name>,<header-name>,…

Directives

<header-name>
- : A sorted list of unique, comma-separated, lowercase HTTP headers that are included in the request.

Examples

Access-Control-Request-Headers: content-type,x-pingother

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Reason: CORS header 'Access-Control-Allow-Origin' does not match 'xyz

Reason: CORS request did not succeed

Reason: CORS disabled

Reason: CORS request external redirect not allowed

Reason: invalid token 'xyz' in CORS header 'Access-Control-Allow-Headers

Reason: invalid token 'xyz' in CORS header 'Access-Control-Allow-Methods

Reason: Did not find method in CORS header 'Access-Control-Allow-Methods

Reason: expected 'true' in CORS header 'Access-Control-Allow-Credentials

Reason: missing token 'xyz' in CORS header 'Access-Control-Allow-Headers' from CORS preflight channel

Reason: CORS header 'Access-Control-Allow-Origin' missing

Reason: Multiple CORS header 'Access-Control-Allow-Origin' not allowed

Reason: Credential is not supported if the CORS header 'Access-Control-Allow-Origin' is '*

Reason: CORS header 'Origin' cannot be added

Reason: CORS preflight channel did not succeed

Reason: CORS request not HTTP

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Content Security Policy: The page's settings blocked the loading of a resource: xyz

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Access-Control-Allow-Credentials header

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Access-Control-Request-Headers header

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