Is there a way to fetch() with headers, WITHOUT forcing header keys to lowercase?

Title. I'm trying to create an API wrapper for a service which uses "Incapsula" as their firewall or something like that.
Issue is, when making a fetch()fetch() request through Deno, the request gets blocked, with the exact same required header and parameter structure as done through say a web browser (simple GET) or an API testing app.

I noticed that the flushed HTTP headers are forced lowercase (which is good, in most cases), which I feel like is causing issues with this very specific API (specifically, only my Deno requests are blocked).

Any way to flush headers as-is? (Or is a custom request/fetch library required for this)