Access Xbox Live features with the Xbox UWP export option, including sign in, presence, achivements and title storage. Requires r374+.
At the moment this is the only viable option for us, as it depends on WebView2, which Microsoft have released only for UWP. If they released it for GDK we'd support that too. As there is no other alternative for us, perhaps if you ask Microsoft they will make an exception - I would guess it's just a policy they have and not a technical requirement.