They are required to identify, to the extent possible, pretty much anyone they talk to - just in case a report comes back an hour later reporting a crime by someone fitting your description, or they become aware of an arrest warrant with your name on it. You do have to tell them who you are, but you are ONLY required to show them a physical ID if you are accused or suspected of an offense. Even so, even if they're not prepared to accuse you of doing something, it's best to show them an ID if you have one on you - simply because if you tell them you don't have an ID on you and it later comes out that you do, you can be charged with lying to a cop.