No sane person would use their personal logins or private keys for customer work. Create ones for that project! Yes, it is a pain but having a bunch of expensive lawyers breathing down your neck is an even bigger one!

You want to separate your customer's work from your personal or other clients' data, even if they don't install any spyware on your computer. How are you supposed to ensure that you don't accidentally breach any NDAs (that you, no doubt, had to sign) if you are commingling the stuff?