Http challange on port 25?

[petercooperjr]

@jvanasco

Wishlist: I think it would be useful to propose a general "privileged port" ACME challenge that could only be run by Root/Administrator, and would either run on a dedicated port or be configured to run on anything under 1024 (assuming windows respects those assignments as well).

I think that in practice this kind of system might as well just use port 53 (DNS), and there are clients like agnos which can fulfill DNS challenges. It's basically "standalone" mode just for DNS instead, just CNAME the _acme-challenge name to the same system you're getting a certificate for, and the client takes care of everything.