A proof of authentication post is a post that you have to make in this bounty thread. It prooves that you really own the bitcointalk account you want to link to your twitter or Telegram account.
Glad rules like this one is being applied I had already experience that my account is use by other user in joining such campaigns. Hope all campaign which applcation is process by fillingg up mere google docs has this kind of veification. Thanks Sylon. By the way, i joined twitter campaign.