-- A token issued for a tunnel key (novox/hq ADR 0169).
--
-- A machine that joins through the tunnel makes its key first, and the token is issued for it: the
-- hub is told the key before the token is shown. So enrolment must take that key and no other — a
-- different one is a machine the hub does not know, offering a tunnel that would never answer. Null
-- for a token issued without one, which enrols as before.
alter table enrolment_token add column overlay_key text;