asp.net mvc - Should I decouple MVC from WebAPI 2 -

i have situation i'm having difficulty in choosing best approach.

i need create/design 3 systems : system : 1 supposed api/mvc ui web application handle business data.

system b : consuming , sending data system

(possibly) system c : centralized login/token server

so @ moment have been thinking of decoupling mvc webapi , have them within same domain i.e. http://server.com/ui , http://server.com/api

system b finished here need investigate in logic authorization , consumption

system c : apis thinking of using jwt centralized user login have no idea how handle login on system authenticated on system a

any guidelines approach appreciated!

thanks raf