Is it somehow possible to use cert-manager with an ACME HTTP01 challenge (specifically Let's Encrypt) and let cert-manager provide the solution via a normal Nginx server instead of Nginx ingress?
So technically it would be enough if cert-manager would write the challenge solution to a file, serving it via Nginx is something I can configure manually.
I see you are trying to make cert-manager to write the challenge solution to a file.
If you dig a bit in the code of cert-maanger, you can see that cert-manager after receiving the challenge, creates a pod (http server), ingress and service for it.
There is no way to get the challenge and write it to a file without modifying the code.