Could not open a connection to your authentication agent.
If you ran into a message "Could not open a connection to your authentication agent." when type ssh-add, it must be that you don't have settings for ssh-agent.
$ ssh-agent SSH_AUTH_SOCK=/var/folders/sx/5z2568ss68997plzhw6qympw0000gn/T//ssh-9ikR207fRO4n/agent.64887; export SSH_AUTH_SOCK; SSH_AGENT_PID=64888; export SSH_AGENT_PID; echo Agent pid 64888;
Then you have to set it up.
If you type
ssh-agent, it prints like the above.
$ eval `ssh-agent` $ ssh-add Identity added: /your/home/.ssh/id_rsa (/your/home/.ssh/id_rsa)
You can evaluate the output. That worked, great.