Hello @jsaarela,
The source code indicates (quick check) that whenever the --docker.tls option is active, the traefik built-in http client switches to https
That is correct. This is when you require TLS Authentication to communicate with your docker or swarm daemon.
Sorry we cannot use letsencrypt but have to use non-self-signed certificates from a commercial source.
For protecting your docker daemon? It is unlikely that you would have a public certificate for this purpose, due to the DNS and other configuration required.