Deployment scenario

I am building an app that will do online job applications. I am
starting my UML modeling of the app and realized that one portion of
the app will be only available internally, while the rest of the app
will be external through our public website. What is the best method of
building the app that will spam multiple locations like this?

While building the Use cases for the app, 5 use cases are internal, 5
external and 1 use case that is shared between the two different
actors. would I want to build that single use case in an entire
different assembly? or perhaps a webservice would solve my problem
here?

thank yuou