SSH key agent forwarding. COPIED FROM https://help.github.com/articles/using-ssh-agent-forwarding

ssh-agent-forwarding.md

see https://help.github.com/articles/using-ssh-agent-forwarding

local

ssh -T git@github.com
# Attempt to SSH in to github
# Hi username! You've successfully authenticated, but GitHub does not provide
# shell access.

echo "$SSH_AUTH_SOCK"
# Print out the SSH_AUTH_SOCK variable
# /tmp/ssh-4hNGMk8AZX/agent.79453

local ~/.ssh/config

Host somewhere.com
  ForwardAgent yes

remote (somewhere.com)