And it's specifically that too. If I delete "Linux" from the UA and resend the request, it succeeds. If I delete just the 'x' off the end, it succeeds. If I lowercase the 'L' it fails. They are deliberately blocking Linux users from managing their Apple ID if they have one.
@Shamar@zalandocalrissian@alexbuzzbee Something I noticed when reading that: the file conversions incorporated into it are for us maintained separately. The ones maintained with CUPS are Mac OS-specific.
So far the core can still be compiled for Linux-based systems. But it is worrying.