But, in the meantime, have you some hint about the inclusion of the app in a MVC app that manages the user authentication? For now, the app and the MVC website are two separate things, and there is perhaps a way to share js variables and functions by including the index.html in a MVC view by rendering his content using razor helpers.
I think this is different from app-inside authenticating the user. It is precisely what I would not to do: the app is working inside the website context and must make use of it.
Sorry, my English is not so good to better explain the problem.
I've already tested the inclusion of the index.html in a ASP.NET MVC view with some success, not yet tried to put a js func in it and call from the app, but I think this is possible, as the view is rendered as an extended index.html, containing the function that I would call.