[Akronymus]

> First, you need to make sure Minecraft is installed on your device. Once this is complete, log in to the launcher while you are still online. This will save your login details for offline access.

It still requires an initial authentication.

[JacobKfromIRC]

A connection to Microsoft's servers will also be required to download the game in the first place, so I'm not sure this is really a problem (for compliance with the bill). I think the official launcher won't even let you download the game without authenticating first, but I'm not sure.