在ASP.NET MVC中使用表单身份验证自定义IPrincipal

This should be simple, but I simply cannot figure it out after all my googling. Here's what I want. I have a custom Users table (no roles at the moment) that I'd like to authorize against. For this I'll have to implement a custom Membership Provider which I've already done. My question is though, how do I go about setting a custom IPrincipal to the HttpContext.Current.User? Where should that happen? Let's say I have the following setup:This should be simple, but I simply cannot figu