Achieved by passing the BUILD_TLS=yes option to
make. As documented by https://redict.io/docs/usage/security/encryption/.
It is also necessary to add openssl as a run time dependency for the alpine image/container (what is the generic, non docker terminology here?) and libssl as a build time and run time dependency for the debian container.
The alpine container, as it appears in this PR, is how we're currently running redict in production. We've only just started doing that mind you, so I can't say for certain that there are no subtle bugs...