This is an e-file Signature Authorization, which is not used when you do a self-prepared return in Turbotax.
Form 8879 is not used when you file your tax return yourself with TurboTax. You don't have to authorize yourself to file your own tax return. Form 8879 is used only to authorize a paid tax preparer to file your return for you. If someone is asking you for Form 8879, either they think you paid someone to do your tax return, or they don't understand how tax returns are filed.
Form 8879 is not included in TurboTax because it is never used when you file with TurboTax. You could try explaining to the person who's asking for it that you filed by yourself. If that doesn't work, and you'd rather just make them happy instead of trying to convince them, here's what you could do. Download the form from the IRS web site. Fill in the top part, and parts I and II. Print the filled-in form and sign Part II. Make a photo copy of the signed form and give the copy to whoever is asking for it.