please to got https://gitlab.com/ulrichSchreiner/caddy-docker for latest code
This is a base image to build the caddy server. It can be used as a base image if you want to have custom plugins in your caddy server.
Create a directory with a Dockerfile and a plugins.go file where you must code the plugin paths of your plugins you want to have in your caddy server.
As an example you can take a look at my caddy-http repository where i build a caddy server with the prometheus and a git plugin.