[5/15] Add exponential backoff to auth attempt rate limiting - #158
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[5/15] Add exponential backoff to auth attempt rate limiting#158UnknownJoe796 wants to merge 2 commits into
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UnknownJoe796
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Jul 29, 2026
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| if (ct >= count) { | ||
| val block = blocked.coerceAtLeast(expires) | ||
| val baseBlock = blocked.coerceAtLeast(expires) |
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This code feels very awkward
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constrainAttemptRate was a flat counter+block window: once a block lapsed, the counter TTL expired and an attacker got a fresh full batch of attempts (slow "popcorn" brute force). Now each time the limit is hit the block doubles (blocked * 2^level) up to a maxBlocked cap (default 3h), and the strike level is persisted under "$cacheKey-level" with a memory far longer than any single block window. A successful action clears both the counter and the level, so legitimate users are never penalized. First-offense behavior (level 0) is identical to before, and the exponent is capped so the Duration math can't overflow. Follow-ups noted for later: password/TOTP/backup-code limiters key off un-normalized input (case/whitespace can dodge the limit), and per-IP limiting needs sourceIp plumbed into typed handler implementations. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> (cherry picked from commit ef55541) (cherry picked from commit e193629)
Three names (blocked / baseBlock / block) referred to the same block duration as it moved through the function, and the invariant that the block window must be >= the attempt window was duplicated, unexplained, in two branches. Names the concepts once (baseBlockDuration, attemptsSoFar, strikeLevel, maxBlockDuration, blockDuration) and splits the escalation/cap expression into two commented steps. No behavior change. (cherry picked from commit 5af890d)
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Replaces the flat rate-limit window on auth attempts with exponential backoff.