title: What defines an unknown source in Android Auto
body: <p>Currently,</p>
  <p>My team and I are developping an Android Auto enabled app. And it appears to me this app is only available in my car unit, when I enable unknown sources in the Android Auto app.</p>
  <p>However I'm wondering what defines an unknown source and how do I make sure my app is not an unknown source. Does Android Auto communicate with the Google Play Services for this or do i need to sign the APK with specific data?</p>