To get the currently logged in user in MVC5, all we had to do was:
using Microsoft.AspNet.Identity; [Authorize] public IHttpActionResult DoSomething() {
I have put something like this in my Controller class and it worked:
IdentityUser user = await userManager.FindByNameAsync(HttpContext.User.Identity.Name);
where userManager is an instance of Microsoft.AspNetCore.Identity.UserManager class (with all weird setup that goes with it).