Prerequisites:

1. Set-up and deploy Caddy Server according to your preferences, preferably on a dedicated server.

2. Set "proxy_mode = True" in your odoo.conf file

3. Make sure you have installed werkzeug Version 0.11 or higher (Ubuntu 18.04 provides werkzeug 0.10.4 only). Example for Ubuntu 18.04 and Odoo 11.0 or higher (Python 3):
   

sudo -H pip3 install werkzeug -U

For Odoo versions < 11.0 use "pip" instead of "pip3".

As long as this feature request is not implemented, the preset "transparent" of the Caddy proxy directive is not sufficient to work properly. The argument "header_upstream X-Forwarded-Host {host}" must be added manually.

See a sample Caddyfile for a successful Odoo proxying with automatic SSL:

example.com {
  redir https://www.example.com
}

www.example.com {
  proxy / http://xxx.xxx.xxx.xxx:8069 {
    transparent
    header_upstream X-Forwarded-Host {host} # transparent preset is not enough

#   header_upstream X-Odoo-dbfilter databasename # in case you use dbfilter_from_header
    }

#  proxy /longpolling http://xxx.xxx.xxx.xxx:8072 { # in case you use it
#    transparent
#    }

#  realip cloudflare (only in case you use cloudflare as CDN)

  gzip
  log /var/log/caddy/example.access.log
  errors /var/log/caddy/example.error.log

#    tls {   (only in case you use Cloudflare as CDN)
#    dns cloudflare
#    }

}