Request for two-factor authentication (2FA)

[patsytau]

Is your feature request related to a problem? Please describe.
This is not a problem :)

Describe the solution you'd like
I would like the ability to enable and required two-factor authentication based on an authenticator app (rather than, say, SMS).

Describe alternatives you've considered
I have used a VPN to access this service, but it is an extra hoop to jump through and affects my PC's networking (especially if I am already connected to a VPN), making it less appealing. It also means that if I wish to share access to this server with somebody then I need to give them VPN access to my network, which isn't ideal.

Additional context

• I use a reverse proxy that handles SSL certificates and port redirection, allowing me to use a simple, clear hostname and still get encrypted traffic.
• I understand that the security of the server is (and can only be) a good-faith, best-effort approach.