Sigh. Although access to the door is absolutely worthless in preventing crew mischief, because if a pilot has murderous intent he will be able to destroy the aircraft in a myriad ways, if you *must* go on about the door, here is a solution for you.
Lock the passengers in.
They're the threat the door is supposed to guard against, no?
Move the door back so it seals off the cabin, where the threat is.
Then we can have an open cockpit, walk around, stretch our legs and aching backs, chat with the crew and enjoy our jobs a bit more. Its not good for my mental health to be locked into a 2x2m room 12 hrs a day.