How to design intranet to have individual .Net modules

We have a number of  mvc.net internal applications we want to consolidate into our intranet and are not sure the best approach is for this.  

We expect create an MVC Intranet app which would display all applications the logged on user has access to based on their AD credentials.  So for example, a Customer Services user would have access to the Order Entry, Product Details, and Customer History applications

What we are unsure of is how to seamlessly transition to that application such that the user does not have to log in again.  Instinctively we see value in keeping the applications as separate MVC projects that we can update without changing the intranet app itself.

I realize this is not a concise question but we are struggling a bit here to state our situation clearly..