An unauthenticated attacker could guess a real device_id and 429-lock that
camera by hammering /api/events before HMAC verification ran, dropping its
accident events. Add a cheap pre-auth per-IP limiter (Config::ingestIpRateLimitPerMin,
default 300/min) that fires before any device-secret lookup, and move the
existing per-device limiter to run only after HMAC + timestamp + nonce checks
succeed, so only authenticated requests consume a device's own quota.
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