ssh's ForwardAgent only works with keys protected by password on osx

Because ssh-agent loads keys from Keychain Access when it starts, and only these keys protected by password will be saved to Keychain Access.

You can check which keys are available to ForwardAgent by ssh-add -l.

You can add a key to ssh-agent and store the passphrase in Keychain Access with one command: ssh-add -K [file].