Who should obey a traffic light?
Anyone driving a vehicle or riding a bicycle should obey a traffic light.
How should you react when a traffic officer tells you to do something witch is ordinarily considered to be against the law?
It depends on what you are asked to do. In a circumstance where an officer is directing traffic at an intersection and you are directed to go while the light is red, you would obey the officer, as officers directing "trump" signals. If you are directed to do something that makes no reasonable sense, such as to hurt someone, you should refuse.