Biggest change is no longer using standard library's tls.Config.getCertificate function to get a certificate during TLS handshake. Implemented our own cache which can be changed dynamically at runtime, even during TLS handshakes. As such, restarts are no longer required after certificate renewals or OCSP updates.
We also allow loading multiple certificates and keys per host, even by specifying a directory (tls got a new 'load' command for that).
Renamed the letsencrypt package to https in a gradual effort to become more generic; and https is more fitting for what the package does now.
There are still some known bugs, e.g. reloading where a new certificate is required but port 80 isn't currently listening, will cause the challenge to fail. There's still plenty of cleanup to do and tests to write. It is especially confusing right now how we enable "on-demand" TLS during setup and keep track of that. But this change should basically work so far.
By separating scheme and port at the parser, we are able to set the port appropriately and also keep the semantics of the scheme being specified by the user later on. The parser also stores an address' original input. Also, the config refactor makes it possible to partially load a config - valuable for determining which ones will need Let's Encrypt integration turned on during a restart.
We had to hack some special support into the server and caddy packages for this. There are some middlewares which should only execute commands when the original parent process first starts up. For example, someone using the startup directive to start a backend service would not expect the command to be executed every time the config was reloaded or changed - only once when they first started the original caddy process.
This commit adds FirstStartup to the virtualhost config
Addresses which fail to resolve are handled more gracefully in the two most common cases: the hostname doesn't resolve or the port is unknown (like "http" on a system that doesn't support that port name). If the hostname doesn't resolve, the host is served on the listener at host 0.0.0.0. If the port is unknown, we attempt to rewrite it as a number manually and try again.
