It looks like the old version of the maas CLI (the on packaged for apt on Ubuntu 18.04) supports adding an SSH key for a user. There are lots of docs on the web about how to do this with the “maas sshkeys” command.
My understanding is that this version of maas-cli is obsolete and the one that can be installed via “snap install maas-cli” is the supported version. This new version does not appear to have an sshkeys command. Has this functionality moved?