MAAS doesn't support SSL natively and needs to be enabled in web server software independently (e.g. Apache, Nginx) which users access directly.
Once the above is done, change the MAAS URL:
sudo maas-region local_config_set --maas-url https://localhost:5240/MAAS sudo systemctl restart maas-regiond
Note that currently Apache is employed for redirecting TCP port 80 to 5240. This may be removed in future versions of MAAS.