There is no document specific to the API for User ID.The only change to the API functionality in 4.1 is the addition of the ability to add your own SSL certificate to the agent. If you want to see other examples of how to use the API I would recommend the gripping and well written document https://live.paloaltonetworks.com/docs/DOC-1936. It applies to both 4.0 and 4.1.
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