Add drift tolerance to one time password checks - #9437
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Codes were verified with no drift, so one was rejected the instant its 30 seconds window ended. RFC 6238 recommends comparing against past timestamps within the transmission delay, allowing at most one step. Default the drift to 15 seconds - half a step. so we accepts the code that has just expired for the first 15 seconds of the next step. Nothing becomes replayable: authenticate_totp still passes otp_last_used_at as `after`, so ROTP drops any step at or before the one already used, and OtpRateLimit still caps repeat attempts. This fixes flaky tests where codes rolled over into the next window.
chrismytton
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Aug 6, 2026
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chrismytton
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Looks good to me! Just one suggestion for a potential code simplification, but no blockers.
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+1122
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| def expiring_code | ||
| code = nil | ||
| travel_to(period_end - 1.second) { code = user.otp_code } | ||
| code | ||
| end |
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Looks like #travel_to returns its block's value, so this can be simplified a bit.
Suggested change
| def expiring_code | |
| code = nil | |
| travel_to(period_end - 1.second) { code = user.otp_code } | |
| code | |
| end | |
| def expiring_code | |
| travel_to(period_end - 1.second) { user.otp_code } | |
| end |
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Codes were verified with no drift, so one was rejected the instant its 30 seconds window ended.
RFC 6238 recommends comparing against past timestamps within the transmission delay, allowing at most one step.
Default the drift to 15 seconds - half a step. so we accepts the code that has just expired for the first 15 seconds of the next step.
Nothing becomes replayable: authenticate_totp still passes otp_last_used_at as
after, so ROTP drops any step at or before the one already used, and OtpRateLimit still caps repeat attempts.This fixes flaky tests where codes rolled over into the next window.