auth: fixes errors when adding a new device after removing devices

[michaelkamphausen]

I ran into the error "Can't decrypt link: don't have the correct keyset" while trying to join with a new device after I removed other devices of the same user. I observed that the new device cannot decrypt the whole team graph because it can only unlock the latest generation of team keys using the latest generation of user keys. These were the only user keys that the new device received on joining, while there have been several generations of user and team keys since the key rotations following the device removals.

My proposed solution is to put all generations of user keys in lockboxes when creating a device invitation, so the new device can unlock all generations of team keys.

With these changes, the next thing I had was an ENCRYPTION_FAILURE when the new device started to sync with the server after joining, because the server was still using generation 0 user keys when talking to the new device. It turned out that the user keys in team.state.members and context.user were not updated after the key rotation when removing a device, so I changed that.

[michaelkamphausen]

When I joined as a new member, I had the same problem with decrypting the links of the team graph after the team keys had previously been rotated. I found that the new user could only unlock the last generation of team keys with his user keys. My suggested solution is to store all generations of team keys in lockboxes encrypted with the new member's user keys.