used to go into System Customization/Custom Shells and enable bash for Email, FTP and SSH and set it to default, clearing the default for whatever other shell might be enabled for admin. I provisioned a new system recently and did the same thing version on 4.18.gpl. But the dropdown box for Other User Permissions includes Email only, Email and FTP, and Email and SCP. No SSH access.
If you select scp, the password file include /usr/bin/scponly in the login shell field. Changing this field to /bin/bash causes it to work, sort of.