How to set up UFW port forwarding from non-privileged port to port 22 on the same computer

On my Ubuntu server, I am running an SSH server (port 22). I want to set up UFW such that all incoming connections are blocked, except through port 12345. External traffic arriving at port 12345 should be forwarded to port 22. How do I set this up using UFW?

Note that I want the SSH daemon's listening port to remain at port 22, because I do not want to run an SSH server on a non-privileged port (12345).