帮助解决ASP.NET MVC和自定义安全设计两部分问题

I'm using ASP.NET MVC and I am trying to separate a lot of my logic. Eventually, this application will be pretty big. It's basically a SaaS app that I need to allow for different kinds of clients to access. I have a two part question; the first deals with my general design and the second deals with how to utilize in ASP.NET MVCI'm using ASP.NET MVC and I am trying to separa