I just spent the last two days researching and implementing the new ASP.NET Identity system with my existing database. More on that here: Integrating ASP.NET Identity into E
Did you remember to put your application name in your web config?
Use one of the following in your controllers.
[Authorize] //Anyone with authorization
[Authorize(Roles="Administrator")] //Admin role only
You could also do something like this.
HttpContext.User.IsInRole("Administrator")
UserManager.IsInRole(userID, "Administrator")