California law: at what point is requiring ID legally justified?

I'm planning on going into law enforcement in Los Angeles, California and am looking into California law. At what point, as a police officer, would actually REQUIRING ID from someone be legally justified? From what I've read, for example, someone not driving a vehicle, walking on a sidewalk, shopping... show more I'm planning on going into law enforcement in Los Angeles, California and am looking into California law.

At what point, as a police officer, would actually REQUIRING ID from someone be legally justified?

From what I've read, for example, someone not driving a vehicle, walking on a sidewalk, shopping in a shopping mall or convenience store would not be required to show their identification to a police officer, unless it's legally justified.

At what point are civilians required to show law enforcement officers their identification? I would truly appreciate if you guys would cite links/sources to California law pages!

Help is appreciated. Thanks guys!
Update: @ Bruce... What are some situations that include reasonable suspicion that would permit them to require the person to identify themself?
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