From 27c06a6e0699f92bcd02b9e930dc8191ab87305e Mon Sep 17 00:00:00 2001 From: "Michael[tm] Smith" Date: Wed, 23 Jun 2021 19:25:03 +0900 Subject: Drop Origin & Accept from Access-Control-Allow-Headers value (#10114) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit * Drop Origin & Accept from Access-Control-Allow-Headers value This change drops the Origin and Accept header names from the value of the Access-Control-Allow-Headers response header sent by Synapse. Per the CORS protocol, it’s not necessary or useful to include those header names. Details: Per-spec at https://fetch.spec.whatwg.org/#forbidden-header-name, Origin is a “forbidden header name” set by the browser and that frontend JavaScript code is never allowed to set. So the value of Access-Control-Allow-Headers isn’t relevant to Origin or in general to other headers set by the browser itself — the browser never ever consults the Access-Control-Allow-Headers value to confirm that it’s OK for the request to include an Origin header. And per-spec at https://fetch.spec.whatwg.org/#cors-safelisted-request-header, Accept is a “CORS-safelisted request-header”, which means that browsers allow requests to contain the Accept header regardless of whether the Access-Control-Allow-Headers value contains "Accept". So it’s unnecessary for the Access-Control-Allow-Headers to explicitly include Accept. Browsers will not perform a CORS preflight for requests containing an Accept request header. Related: https://github.com/matrix-org/matrix-doc/pull/3225 Signed-off-by: Michael[tm] Smith --- changelog.d/10114.misc | 1 + 1 file changed, 1 insertion(+) create mode 100644 changelog.d/10114.misc (limited to 'changelog.d/10114.misc') diff --git a/changelog.d/10114.misc b/changelog.d/10114.misc new file mode 100644 index 0000000000..808548f7c7 --- /dev/null +++ b/changelog.d/10114.misc @@ -0,0 +1 @@ +Drop Origin and Accept from the value of the Access-Control-Allow-Headers response header. -- cgit 1.5.1