I'm developing an OpenXR app with C++ on top of the Windows Mixed Reality OpenXR runtime. I need to directly access the proximity sensor in the headset. In general this should be somehow possible because I basically have it running when using SteamVR as OpenXR runtime and the Windows Mixed Reality Plugin. In this case I can create an input binding in SteamVR for a windows mixed realtiy HMD and map the proximity sensor to a button press.
So the SteamVR Windows Mixed Realtiy plugin in steam is somehow able to get access to the proximity sensor. But I cannot find any information about how to access windows mixed reality inputs from c++ code.
I could imagine that there might be an undocumented OpenXR input action path like /user/head/proximity or something. I also looked at C:\Program Files (x86)\Steam\steamapps\common\MixedRealityVRDriver\bin\win64 and there seems to be a Microsoft.MixedReality.Input.dll but I could not find any information about this on Microsoft API docs.
I would really like to not have to use SteamVR to access the proximity sensor as I'm writing an industrial application where requiring a steam account isn't an option.