The current user or worker could be retrieved through following code since AX 2012
DirPersonUser::currentWorker()
However, In Dynamics 365 for operation this has refactored to;
HcmWorkerLookup::currentWorker()
DirPersonUser::currentWorker()
However, In Dynamics 365 for operation this has refactored to;
HcmWorkerLookup::currentWorker()