Authorization using Entity Framework in ASP.NET MVC
You should not instanciate a new DbContext each time your code go throw your ActionFilter.  What you should do is to use dependency injection and to define an execution scope.

Because you are using .net Framework and not .net core, I advise you to look into DI providers such as Autofac or Ninject.

I advise you to look into why to use DI and think about what execution scope you need (probably perScope() in your case).

Hope it helps.