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Access-Control-Expose-Headers

The Access-Control-Expose-Headers response header indicates which headers can be exposed as part of the response by listing their names.

By default, only the 7 CORS-safelisted response headers are exposed:

If you want clients to be able to access other headers, you have to list them using the Access-Control-Expose-Headers header. Content-Length was not part of the original set safelisted response headers [ref].

Syntax

Access-Control-Expose-Headers: <header-name>, <header-name>, ...
Access-Control-Expose-Headers: *

Directives

<header-name>
A list of exposed headers consisting of zero or more header names other than the CORS-safelisted request headers that the resource might use and can be exposed.
* (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

To expose a non-CORS-safelisted request header, you can specify:

Access-Control-Expose-Headers: Content-Length

To additionally expose a custom header, like X-Kuma-Revision, you can specify multiple headers separated by a comma:

Access-Control-Expose-Headers: Content-Length, X-Kuma-Revision

In requests without credentials, you can also use a wildcard value:

Access-Control-Expose-Headers: *

However, this won't wildcard the Authorization header, so if you need to expose that, you will need to list it explicitly:

Access-Control-Expose-Headers: *, Authorization

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
Access-Control-Expose-Headers 4 12 3.5 10 12 4
Wildcard (*) 65 79 69 No 52 No
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
Access-Control-Expose-Headers 2 Yes 4 12 3.2 Yes
Wildcard (*) 65 65 No 47 No 9.0

See also

© 2005–2020 Mozilla and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Expose-Headers