I looked at the c# code on github. it seems that the authenticationContext ctor param is never used.
every request will start with:
var requestContext = request?.AuthenticationContext ?? authenticationContext
but, requestContext will never be used.
request.AuthenticationContext (all of them) are also never used.
I guess it was planned to bind a ServerInstanceAPI to a specific user.
=> I would like that very much.
it would prevent us from having to specify a PlayFabId for every request.