Just a note of warning: kobowiki.org is not official documentation and doesn’t seem to be up-to-date.
I can’t speak specifically to wildcards, but GitHub - kobotoolbox/kobo-install: A command-line installer for setting up and running KoboToolbox on a remote server or local computer, using kobo-docker. has recently been updated to support automatic certificate generation with Let’s Encrypt. As long as your DNS resolves publicly, it should configure SSL easily. Here’s my experience setting it up on a $10/month VPS:
