https://github.com/hoverkraft-tech/compose-action/blob/2ab47e7e09da3e8e47398d6c26b9bd345071a442/dist/index.js#L25988
// https://fetch.spec.whatwg.org/#append-a-request-origin-header
function appendRequestOriginHeader (request) {
// 1. Let serializedOrigin be the result of byte-serializing a request origin
// with request.
// TODO: implement "byte-serializing a request origin"
let serializedOrigin = request.origin
// - "'client' is changed to an origin during fetching."
// This doesn't happen in undici (in most cases) because undici, by default,
// has no concept of origin.
// - request.origin can also be set to request.client.origin (client being
// an environment settings object), which is undefined without using
// setGlobalOrigin.
if (serializedOrigin === 'client' || serializedOrigin === undefined) {
return
}
// 2. If request’s response tainting is "cors" or request’s mode is "websocket",
// then append (`Origin`, serializedOrigin) to request’s header list.
// 3. Otherwise, if request’s method is neither `GET` nor `HEAD`, then:
if (request.responseTainting === 'cors' || request.mode === 'websocket') {
request.headersList.append('origin', serializedOrigin, true)
} else if (request.method !== 'GET' && request.method !== 'HEAD') {
// 1. Switch on request’s referrer policy:
switch (request.referrerPolicy) {
