If I have a host I want to be able to connect to and I currently have a keyboard and monitor plugged in, how would I copy a key to a user so I can connect as that user remotely. Essentially I want to do the same thing as ssh-copy-id but without having to be able to connect over ssh first.
The keys are stored in a text file under ~/.ssh/authorized_keys
To add a new key just copy the contents of the *.pub file of your key to a new line in this file.
Some more information is available here https://www.ssh.com/ssh/authorized_keys/