If you CC and an officer discovers this then you must show your CPL. If you OC in a conceal free zone (school, hospital etc.) you would be required to prove you have a CPL to exempt yourself for that particular area.
If you OC in your normal daily activity and you are stopped and asked for ID simply because you a carrying a firearm and you are not in a vehicle nor in a conceal free zone, then there is NO obligation to provide any type of ID. You can say "No thanks, have a nice day.' Then calmly walk in the opposite direction.