[9front] acmed: dns support.

[9front] acmed: dns support.

[ori]

Today, I finally finished adding dns support
to acmed.

To use it, you'll need to have a functioning
DNS server running.

Then, when you tell it to use dns, acmed will
write a snippet that defines the required dns
records. By default, this will be put into:

	/lib/ndb/dnschallenge

which you will need to include with:

	database=
		<...previous contents...>
		file=/lib/ndb/dnschallenge

 From there, you just run acmed as usual, but
with an additional parameter so that it knows
the domain name:

	acmed -t dns	\
		you@example.com	\
		/path/to/csr	\
		domain.com

and it will handle generating the challenge
and telling the dns server to refresh.

Caveat: this needs to run as the same user
as the dns server (typically hostowner).

Other than updating the manpage with an
example of doing a DNS challenge, I think
that this is more or less ready to commit
to 9front.