fix: uppercase origin header

[n3oney]

While HTTP headers should be case-insensitive, unfortunately some servers don't conform to that behavior. Unfortunately, the http crate always stores headers in lowercase without any way to prevent that behavior, so if we run into a server that does not conform to spec, we're doomed.
This is a workaround to that issue - it changes the origin header into Origin.

[daniel-abramov]

Hm, alright, let's merge it! This is a second header for which we implement such a workaround, perhaps we would need to find a generic solution for it (similar to how hyper handled it once) since it's not clear how many other headers will be ignored by the server for the same reason (the server that performs a case-sensitive check of a single header is likely to do the same for all other headers as well).

[n3oney]

Hm, alright, let's merge it! This is a second header for which we implement such a workaround, perhaps we would need to find a generic solution for it (similar to how hyper handled it once) since it's not clear how many other headers will be ignored by the server for the same reason (the server that performs a case-sensitive check of a single header is likely to do the same for all other headers as well).

I definitely agree. I think it'd be much better to implement some kind of custom hashmap to handle headers. I know that isahc has a title_case_headers configuration option which as the name suggests turns headers into title case, however that's still very much a workaround, and a full-fledged solution would be appreciated.