problems Integrating an asp.net website into an asp.net mvc 4 application

problems Integrating an asp.net website into an asp.net mvc 4 application

I am creating a asp.net mvc 4 application to replace a suite of existing
projects including an asp.net 3.5 website and windows forms.
I have spent many months developing the asp.net mvc 4 application from
scratch and I have been focusing on the windows forms appliction.
I am now trying to integrate the asp.net 3.5 website....For now I am just
trying to add the website to the project. I have looked for how to do this
and I see most of what I need...but I have a few problems.
I am using areas. For the Carrier area (where the website applies) I have
added a folder called aspnet...and I have added the webpages and the other
code to this folder....All of this compiles.
I have also modified the RoutConfig.Cs file by adding this line:
routes.IgnoreRoute("{resource}.aspx/{*pathInfo}");
When I added the webpages to the project I added just the code, ignoring
the project files and the web.config for the asp.net website.....
I don't think I need to convert over the project files at all...but I am
trying to figure out what to do with the web.config....I know I can have a
web.config in the aspnet folder....but what to put into is my
question.....
I tried just copying the existing file, but it had issues with the
different .net version (website is v3.5 and the mvc application is v4.0 of
.net)....
My big concern is how to handle the security...the website used forms
authentication security and the mvc application uses simpleMembership.
All of the reading I have done focused on converting asp.net web
applications, not websites over to mvc.....and most don't say much about
the web.config file....
Nor have I found what to do with the security...again I have seen some
things on integrating the security model of MVC back into an existing
asp.net web application, but nothing on how to get an asp.net website
working with the mvc simplemembership.
help!!