Force a particular port for particular machine

[santomet]

I am working on a simple API to manage computers that connect to my sish.
Because I want to know exactly which machine has which port and I want to prevent users from changing the remote port in their autossh configurations.

I am using ssh key authentication only - every computer is represented by one key file with filename equal to their id in my database.

It would be nice if I could force the usage of a particular port for a particular computer represented by the key