Yep, when a cop won’t prove he’s a cop then he’s not a cop.
In this context show a badge or something else to prove you’re real.
I would like to see legislation to clarify that anyone who might have reason to doubt the legitimacy of a government agent's actions has the right to question it; one of the duties of a government agent is to dispel any such reasonable doubts, and government agents should not bristle at being asked to do their duty.