This plugin launches a temporary built-in TCP listener that stores the validation details in memory. This requires exclusive access to the port, so it cannot be used while another application is handling connections.
Even though the ACME server will always open the validation connection on
port 443, you may forward that to another port within your internal
infrastructure. Using the --validationport switch you can tell the
plugin to listen to a specific port.
--validationmode tls-alpn-01 [--validation selfhosting] [--validationport 4330]