title: Get Session from HttpActionContext
body: <p>I'm trying to create a permission attribute to configure in each action of my controllers so this custom attribute should take the sessionId from the user.
  My code is like that:</p>
  
  <pre><code>public class PermissionChecker: ActionFilterAttribute
  {
      private int _permissionId { get; set; }
      private IUserSelectorService _userService { get; set; }
  
      public PermissionChecker(int permissionId)
      {
          _permissionId = permissionId;
          _userService = new UserSelectorService();
      }
  
      public PermissionChecker(int permissionId, IUserSelectorService userService)
      {
          _permissionId = permissionId;
          _userService = userService;
      }
  
      public override void OnActionExecuting(HttpActionContext actionContext)
      {
          if (_userService.HasPermission(_permissionId, /* here I must pass the session["Id"]*/)){
               base.OnActionExecuting(actionContext);
               return;
          }
          throw new HttpException(401, "Unauthorized");
      }
  }
  </code></pre>