[MLS] *re*joining a group with the same identity key

["Katriel Cohn-Gordon" <[e-mail]>]

Hi all,

Here'a s case we might want to think about: what should happen if a
*current member* of a group asks to join, with the same long-term key
that they're already joined with?
The simple answer is to forbid such joins, but this might happen if a
device forgets its group state but remembers its identity key. (Perhaps
it writes the group state to a local database and the write got
corrupted.)
Alternatively I see a handful of different ways we could support these
joins, if we wanted to. Perhaps the simplest is to allow the device to
double-join but require it to immediately delete the old copy of itself.
best,
k