Get User Name on Action Filter

Bit late for an answer but this is best solution if you are using HttpActionContext in your filter You can always use it as mentioned here:-

public override Task OnActionExecutingAsync(HttpActionContext actionContext, CancellationToken cancellationToken)
{
   if (actionContext.RequestContext.Principal.Identity.IsAuthenticated)
   {
      var userName = actionContext.RequestContext.Principal.Identity.Name;
   }
}