The documentation for DeviceAuthenticationRequest is not accurate for C#. Many of the functions that it shows under the section "Code Samples" are not valid functions for the DeviceAuthenticationRequest. For example: SetDeviceId(), SetDeviceModel(), SetDeviceName() all do not exist as public functions.
Please review and update the API documentation.
These are actually set by Unity within the PlatformBase.cs script in the Unity SDK. You can override this and set them manually if you'd prefer. It could be made clearer in the documentation alright. Thanks for your input here.