The previous fix had a subtle bug: JavaScript && short-circuits,
so crypto.timingSafeEqual() was skipped when buffer lengths differed
(sameLength was false). The dummy buffer was allocated but never
compared, leaving the original length-based timing leak intact.
Now timingSafeEqual is eagerly assigned to a const before the &&
guard, guaranteeing it runs in constant time on every auth attempt
regardless of whether the length guess was correct.
isAdminMetricsAuthorized() returned early when buffer lengths differed,
allowing an attacker to discover the token length by measuring response
time. Now always calls crypto.timingSafeEqual (using a zeroed dummy
buffer on length mismatch) so every auth attempt takes constant time
regardless of whether the length guess was correct.
Reported-by: Kaia-Alenia
Timo