Ryan,
This is unfortunately true, I was going to suggest using "App Login" workflow, but it would not work, since this would only work for content and services hosted by Esri and consume credits, it would not work for accessing private content or item.
Limitations of App Login | ArcGIS for Developers
Although you cannot use an App login with private content, if your goal is to distribute or sell an app to organizations without ArcGIS Online (no named users), you may control access to your content by using your own login mechanism (I.e. Identity) to the app.
Thank you,
Erwin.