"the difference between..a general worker..checks that a secure door is locked by trying the handle"
Actually I would have described a port scan as exactly like trying the doors on a building you work in.
Not attempting to enter (by your analogy), just test to see if it's open to begin with.
However if you're writing your own authorization letter you should probably include a clause to allow repeat scans whenever there is a significant change in the system, with "significant" being loosely or tightly defined on how awkward your boss is likely to be.
Biting the hand that feeds IT
