There is currently no way to get a list of shared mailboxes or determine whether a User account is actually a shared mailbox. Ideally there would be a new top-level object -- eg., GET /sharedMailbox...
Your reply says ".exe" file. 🙂 Anyway, our goal is to have a simple onboarding and configuration process for our SaaS app. We don't want to create and maintain apps for multiple platforms or the customer to have to download an app or a script or anything else—the app is on the web and, with the appropriate permissions, they should be able to do everything there.