My question would be, why do you want to put a password on grub?
I would remind you that the only way to protect your system or data if one has physical access is with cryptography. If you give me an hour with your computer I will have your entire hard drive posted to the internet. Biometrics, passwords, etc. doesn't matter if it isn't encrypted. Most of that hour will be spent uploading and taking coffee breaks. It isn't that I am that good, it's that it is so easy to get around.
Insanity: Doing the same thing over and over and each time expecting a different result.
Democracy is 2 wolves and a lamb voting on the menu. Liberty is an armed lamb protesting the electoral outcome. A Republic negates the need for an armed protest.