These all are good suggestions, attached updated patch.
> Maybe something like PG_SASL_EXCHANGE_ABANDONED?
This is the only one I wasn't sure of, I used RESTART because I was
focusing more on the intention of the server ("please restart
authentication with this additional information"), and a bit also on
the idea that later restart could stay even within the same
connection, both in this case and if we add support for
reauthentication on token expiration.
On the other hand I'm not 100% sure how the other two would work, and
ABANDONED is a better description for the current situation, so I
adjusted the patch to use that.
