But as a person who rolls LE certs across a very non-happy-path environment (many SAN domains, edge nodes which are geo-balanced).
I have a lot of issues automating this process, right now I have a HTTPd which reverse proxies the .well-known back to a central place where I run certbot and then I push out the cert to the nodes, however, sometimes one of our SAN domains will need to be removed and the whole universe comes crashing down.
DNS-01 Challenge is "nice" (although, doesn't feel super well supported); but requires domains registered with some kind of DNS server that accepts API's to change records, so Amazon route53- but it's exceptionally hard to roll your own DNS in this case. :\
1. HTTP-01 challenges have a "correct" answer for a given Let's Encrypt account which depends only on the challenge (ie the part in the HTTP GET request) and on knowing which account you want to use.
Silently Certbot creates you an account, with a private authentication key and so on, for the Let's Encrypt service. When it gives you a file to prove control by placing it in /.well-known/acme-challenge/ the content of the file is always the same as the filename, plus a suffix that depends on your key.
So long as you use the same account you can thus bake this suffix into the web server, essentially causing it to answer any request from anybody: "Hey, who is allowed to issue for somename.example ?" "dijit is allowed to do that". Bad guys can't use this because they don't know your private account key, but for you now magically everything is authorised, since when it is asked your server will answer "dijit is allowed to do that" to any question it's asked.
2. DNS-01 can be redirected using CNAME. Add a CNAME, once, manually if necessary, to redirect the DNS-01 checks to a DNS server you've set up for this specific purpose.
Besides the multiple commercial DNS providers which certbot has plugins available for there is also a dns plug-in supporting rfc2316 updates. This means it can be integrated with a large number of self-hosted DNS servers. Bind, powerdns and Microsoft DNS are just some of the servers with rfc2316 DNS update support.
But as a person who rolls LE certs across a very non-happy-path environment (many SAN domains, edge nodes which are geo-balanced).
I have a lot of issues automating this process, right now I have a HTTPd which reverse proxies the .well-known back to a central place where I run certbot and then I push out the cert to the nodes, however, sometimes one of our SAN domains will need to be removed and the whole universe comes crashing down.
DNS-01 Challenge is "nice" (although, doesn't feel super well supported); but requires domains registered with some kind of DNS server that accepts API's to change records, so Amazon route53- but it's exceptionally hard to roll your own DNS in this case. :\