The Customs agent insisted he had the authority search the device. I was thinking about this the other day, as a non-American, and I don't see how that is poss

The Customs agent insisted he had the authority search the device. I was thinking about this the other day, as a non-American, and I don't see how that is possible. I work for the Australian gov't and of course cannot give out passwords or access to any of the devices which I carry which belong to the Australian gov't. How does US Border controls deal with that situation. They definitely do not have the authority to search a device owned by a foreign gov't, though it also seems they don't have the authority to search the device of an American either. Thoughts?