Managing Public/Secure applications

My office is using ArcGIS for Server 10.1 and Flex Viewer 3.4, and a relatively new to both. We have already published a few public and secure map services. And we now would like to build an application that uses those services. We have created generic user accounts for accessing these services in our applications, as the users will be getting to the applications from another ASP.NET web application. We would like to know if it is possible to to build our flex application in a way so that public users will only see the public layers, and secured users would see all layers without them having to enter in the generic account login credentials? Or is it best practice to create two separate applications, one for public use and the other for secure use that uses a proxy page?

Thanks!