Fetch API, custom request headers, CORS, and cross-origin redirects

Question

I need to make an HTTP GET request with custom request headers in-browser and process the result as it streams in. The Fetch API is ideal for this:

Answer 1

Supporting redirects to requests that require a preflight is very recent change to Fetch (which defines CORS).

https://github.com/whatwg/fetch/commit/0d9a4db8bc02251cc9e391543bb3c1322fb882f2

I believe some implementations have started adjusting their implementations, but this will take some time to reach everyone.