Would there be anyway to know the origin acount's username that ssh'ed into the server?

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http://serverfault.com – I initially git cloned a repo, when I push my work, within the post-receive hook, I would like to retrieve the origin acount's username who did the push. I know $SSH_CONNECTION and $SSH_CLIENT give me the origin IP, but I can't find a way to get the username of the origin account. Info: The ssh connection is established using the public key / passwordless method (HowTos)