If you own a CA, you could use it a lot with Docker... or not. I mean it could help. For instance, you could use it to secure a vault to store and share secrets. You could rely on a PKI to authenticate clients ans servers. You could also use it to encrypt HTTP protocol, including the access to your private registry. This blog will explore the latter scenario to illustrate how you can leverage your newly created Certificate Authority.
The example below relies on Fedora/Enterprise Linux; if you plan to use Debian, another Linux distribution, Windows or OSX, you should have to adapt the procedure to make it work.