I have just launched a new website, https://www.threenh.com/. I also use this approach: TRAMP defaults to the ControlMaster=auto OpenSSH option, but it will override the ControlPath setting when starting an SSH session. TRAMP does this to avoid lag when the master session opened outside the Emacs session is no longer active. This is why TRAMP prompts for a password again even if an SSH connection has already been established.