Unity Task not working with target Universal Windows Platform,Use System.Threading.Tasks on UWP

I'm trying to develop a Unity project which has to use some UWP API; in order to do this I also have to use Task from System.Threading.Tasks namespace.

The problem is that inside the editor UWP libraries don't work but if I try to build the project for UWP target I got an error which says "Task does not exist in the current context". Task only work if I run the project inside the editor.

How could I use Task and build for Universal Windows Platform? I've set palyer's settings to use the experimental .NET framework 4.6 inside Unity 2017.2.1f1

Has someone already faced this problem or has any advice?

,I want to use a UWP API inside a Unity project, in order to do this I also have to use Task from System.Threading.Tasks namespace.

The problem is that in the editor I'm able to use Task but not to load any UWP namespace; if i try to build for Universal Windows Platform UWP libraries don't generate errors but I can't use the Task class. This is blocking all my project and I'm trying to figure it out.

I've set player's settings in order to use the experimental .NET framework 4.6 in Unity. Anyone has some advice or has already faced this problem?