One meaning of straight for some hundreds of years has been true, correct, right. The use of damn with it is just a modern usage which reinforces the meaning. So, damn straight means "You're certainly correct!"
I very much doubt whether you would be able to find the very first use of such a phrase, but good luck to you!
Sorry, do not know the answer to your question, but have just noticed your name. Do you really like poetry? I have written some, and hope you would like to email me in private. Meet me in the SportsBank if you like?