feat(rate-limit): key by authKey hash, not just IP#65
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express-rate-limit defaults to keying by IP, which has two
problems against an authenticated API:
1. Shared-IP false positives. Mobile-carrier NAT, corporate
egress, a household behind one router, k8s pods sharing a
SNAT — all of these put legitimate clients on a shared
budget. A noisy neighbor poisons everyone else.
2. Brute-force pivot. An attacker rotating source IPs (vps
pool, residential proxy, tor) stretches a per-IP budget
by however many addresses they can spin up.
The new key generator looks at the `authKey` header:
- present → key by `k:<sha256-prefix-of-authKey>`
- absent → key by `ip:<remote_address>` (the brute-force path)
Authenticated clients get their own per-key budget regardless
of egress IP. Anonymous requests (someone fishing for a valid
key) still get per-IP keying — the right granularity there.
Extracted into app/middleware/rate-limit-key.js so the keying
logic is unit-testable. server.js just imports it.
Tests: 7 cases in tests/unit/rate-limit-key.test.js — verifies
deterministic mapping, separation between distinct authKeys, IP
fallback, and that the raw authKey never appears in the
returned key (in case the rate-limiter store becomes redis-
backed later).
Suite: 33 files / 241 passing + 4 integration skipped (was 32 / 234).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
express-rate-limit's default IP keying causes shared-IP false positives (mobile carrier NAT, corp egress) and is easy to dodge by rotating source IPs. Switching to:
k:<sha256-prefix-of-authKey>(deterministic, separates budgets per credential)Extracted into
app/middleware/rate-limit-key.jsfor testability.Test plan
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