All beat patrol officers have been replaced by copbots, BUT administrators and engineers still exist.
Suited up in effective armor and possessing a valuable “Police ID”, these units are very rare and a good deal more resilient than regular zombies.
The “Police ID” means that Copbots and Eyebots will ignore you. As a law enforcement officer, you are clearly allowed to do whatever is needed in the pursuit of your duty.
Police blockades involve a single officer zombie and a number of copbots and robotic “police vehicles” blocking the road.
“Military IDs” convince turrets you are friendly… at a distance. Penetrating a military base is actually a two step procedure, though.
Once you are close enough, a “secondary check” is done to compare you to the military database.
At that point, they “yell stuff about unauthorized use of military/police identification and attack”, in the words of kevingranade, if you don’t match a database entry.
So the second part is to hack the military database to enter your information.
Lacking either piece - the id, or the database entry, means no military base access for you. If you lack the first, you’ll never get close enough to do the database check, after all.