Authorize issue for Custom Roles Based Access Control in MVC

Question

I have implemented below Custom Roles Based Access Control. First time when user going to logg into my web application.

In class RBACAttribute When I put debugger in below class then it is checking whole controlers in my web application (i.e project)

public override void OnAuthorization(AuthorizationContext filterContext)

{

string requiredPermission = String.Format("{0}", filterContext.ActionDescriptor.ControllerDescriptor.ControllerName);

}

Why first time it is checking for all controllers?