When using make-user and passing a private key path, as opposed to a private key literal value, it seems something gets confused and the key doesn't get used properly.
A few snippers illustrating it:
@sundbp Is your key in the keychain (assuming this is on OS X locally)?
Fails either way. I use ssh-agent and ssh-add via scripts, not sure how that and if that hooks into OSX keychain thing (not a long time OSX user), use the same on linux.
OK, sounds like it's not in the OS X keychain then. Note the keychain is distinct from the ssh-agent.
@sundbp I'm closing this. Please reopen if it is still an issue.
Cool. I started manually adding keys to via ssh-add as a principle. Think the auto-add key still is broken but haven't tried in quite a while so can't comment for sure. Either way I have a workaround.