Replace global lockout with an alert and per-IP exponential backoff

[Sloth-on-meth]

Problem

Once 50 failed attempts accumulated in an hour, check_global_rate_limit() rejected every PIN attempt, valid ones included. Anyone could therefore deny the door to all legitimate users for an hour with 50 junk guesses.

Changes

• Removed the hard global lockout. Crossing max_global_attempts_per_hour now writes a GLOBAL_THRESHOLD audit entry and sends one Pushbullet alert per window (record_global_failure, _notify_admin).
• Throttling is per client with exponential backoff: each consecutive block doubles block_time_minutes, capped at 24h, reset on a successful login (next_block_duration). Applies to the keypad and admin login.
• Idle backoff state is evicted by the existing cleanup sweep.

Trade-off

Without the global cutoff, the defences against guessing spread across many IPs are per-IP backoff and the alert. Pairs with #42 (IP-only keying), which makes the per-IP limit hard to dodge.

Tests

tests/test_backoff.py (doubling/cap, first block == block_time, success resets); the old global-lockout test is replaced by tests asserting valid PINs still work past the threshold and exactly one alert is sent. conftest.py resets the new state. Full suite passes (112), ruff clean.

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Summary by CodeRabbit

• Security
  • Repeated blocked sign-in attempts now result in progressively longer lockouts, up to 24 hours. A successful PIN, OIDC, or admin sign-in resets the related lockout history.
  • Failed door attempts, including invalid PIN formats, count toward the hourly failure threshold. Reaching the threshold sends an administrator alert, including a best-effort Pushbullet notification, but does not block otherwise valid requests. Notification delivery failures are logged.

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• app.py
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📝 Walkthrough

Walkthrough

Global failed attempts now trigger threshold logging and best-effort admin alerts instead of a global request lockout. Per-session and per-client blocks use exponential durations capped at 24 hours. Successful authentication clears the corresponding strike counts.

Changes

Authentication rate limits

Layer / File(s)	Summary
Global failure tracking and alerting app.py, tests/test_security.py, tests/test_backoff.py	Failed attempts update the hourly counter. Reaching the configured threshold logs and sends a best-effort admin alert. The global counter no longer blocks requests, and tests verify that valid PIN requests continue at the threshold.
Adaptive block durations and authentication resets app.py, tests/conftest.py, tests/test_backoff.py	Session and client block durations increase per key, with an exponent limit and a 24-hour cap. Successful PIN, OIDC, and admin authentication clear strike counts. Cleanup retains blocked-client state for the maximum block duration. Tests cover duration growth, the cap, successful-login resets, and cleanup.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  actor Client
  participant open_door
  participant record_global_failure
  participant _notify_admin
  participant Pushbullet
  Client->>open_door: Submit invalid PIN
  open_door->>record_global_failure: Record failed attempt
  record_global_failure->>_notify_admin: Notify when threshold is reached
  _notify_admin->>Pushbullet: Send best-effort alert

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Merge Risk: ⚪ Minimal · up to e122b

The change replaces global lockout with per-client backoff and threshold alerts. No unresolved issue in the reviewed scope warrants delaying merge; proceed with normal validation.

Security Architecture Review

Security architecture risk: 🟠 High · up to e122b

Removing the global lockout fixes a denial-of-service problem, but door throttling still depends on changeable request headers and disposable sessions rather than IP alone. A client can obtain many fresh guessing allowances against PINs that authorize physical door access. Administrator alerts do not stop those attempts.

Retained concerns

• High · security · inferred: The global guessing gate is removed before the stated IP-only prerequisite is implemented. An unauthenticated client able to reach /open-door can discard its session cookie and vary acceptable User-Agent or Accept-Language values to select fresh keypad counters and strike histories from the same IP. The composite key predates this PR, but removing the aggregate cutoff makes its weakness materially more exposed. A successful guess authorizes the configured door-opening command; best-effort alerts provide detection, not enforcement.

Security review details

Security Blast Radius

• inferred — The worsened guessing exposure applies to any client able to reach /open-door and to the effective PIN set checked by that service, rather than one named account. A matching PIN reaches a command for the configured Home Assistant entity. No direct administrator grant or arbitrary downstream target selection follows from this path; broader Home Assistant token privileges were not established.

Security Findings and Attack Paths

• inferred — A same-IP requester can omit the session cookie and change header values to obtain fresh session and composite-client buckets. The suspicious-request check accepts sufficiently long User-Agent values without its listed bot substrings, so it does not bind those buckets to a stable identity. The removed hourly gate previously bounded this strategy within each process; alerts now leave authentication reachable.

Trust Boundaries and Controls

• observed — Client identification starts with request.remote_addr under ProxyFix configured to trust one forwarded address, then includes attacker-supplied headers in the keypad enforcement key. Administrator enforcement uses the primary IP instead. Signed-cookie and in-memory active-block checks remain, but the same-IP key-rotation concern does not require forging either a cookie or a source address. Upstream proxy sanitization was not established.

Resilience and Maintainability Implications

• observed — A normal notification failure is logged without rejecting authentication, but the threshold counter has already advanced and subsequent failures do not retry notification in that window. Local audit logging occurs before notification. This makes the replacement control best-effort detection rather than guaranteed delivery or enforcement.
• inferred — Exact once-per-window alerting and consecutive strike progression depend on unsynchronized read-modify-write transitions in process-local state. The inspected tests establish sequential behavior, not concurrent or cross-worker guarantees. This remains a state-ownership uncertainty because production worker topology was not supplied.

Hardening Proposals

• proposed — Establish a stable, trusted IP enforcement key before relying on backoff as the replacement for the aggregate gate. Mutable headers and disposable sessions should not create independent IP allowances. This can preserve the availability benefit without restoring an attacker-triggered global lockout.
• proposed — Define whether throttling and threshold notification must span workers or survive restart, and give those transitions explicit ownership and atomic coordination where required. Keep door and administrator reset authority explicit when sharing session state.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 20 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: replacing the global lockout with alerts and per-IP exponential backoff.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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🤖 Prompt to fix review comments

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Inline comments:
Review comments at @app.py:
- Around line 426-431: Update the Pushbullet alert helper’s requests.post call
to check the response status and surface HTTP errors as alert failures, so
rejected alerts are visible to operators. Use the existing error-handling or
logging path in the surrounding helper.
- Line 468: Update _cleanup_rate_limit_state() to retain rate-limit entries for
at least MAX_BLOCK_TIME plus the existing cleanup buffer, while preserving the
current BLOCK_TIME and one-hour minimums; this ensures cleanup cannot evict an
identifier before its block expires.

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📒 Files selected for processing (4)

• app.py
• tests/conftest.py
• tests/test_backoff.py
• tests/test_security.py

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