Which kind of identification and authentication is used to secure an airplane? What does the pilot use? a password? my wife identifies and authenticates herself to her car every morning using her car keys. I don't see the pilot in movies use a similar key?! I don't expect the designers to leave an airplane open for any attacker to go to the cabinet and fly away.
Most smaller propeller planes have nothing. When you're in you can fly away. This seems to be the same for those private jets and older Boeings. I don't fly planes, but I've seen that Airplane Repo program on Discovery, and they just get in and fly away. How this works with the newest planes - no idea.