As a system administrator (in the technical sense - configuring DNS and talking IPv6 doesn't scare me), I want to set up a custom domain for my church management system (ChMS) so that my volunteers understand the ChMS is an integral part of the church, and can have full trust in the system being served from my domain.
So instead of logging in from elvanto.com (and searching by email) or subdomain.elvanto.com.au, I want my volunteers and staff to login from https://volunteer.church.org.au/
To be explicit, this will require DNS mapping, not a redirect/alias/CNAME.