Lowecased "host" header

We use cloudflare to proxy (DNS: proxied) traffic to our domain ( domain-name for instance ).

But we always receive hostname lowercased at out end.

What we mean:

curl https://domain-name/some-path
triggers our backend with “host” header “domain-name” - it’s ok

curl https://doMain-nAme/some-path
triggers our backend with “host” header “domain-name” again
but we expect “doMain-nAme

can you advise anything?