plenary.curl breaks headers if _ is required in header name

[V1OL3TF0X]

I have a service that requires a header with an _ in it's name. (Think CUSTOM_AUTH_HEADER or smth like that). I wanted to test it through a library that uses plenary.curl, and found that the request returns 404: upon closer inspection it turned out that the culprit is this line:

https://github.com/nvim-lua/plenary.nvim/blob/master/lua/plenary/curl.lua#L101

turning my header into CUSTOM-AUTH-HEADER, therefore making the request invalid. Is there a way to override this? As far as I know the HTTP spec doesn't enforce - over _, so I'd like to have a solution (or at least know why this mapping was made).

Thanks