feat(webhook): verify tiktok ingress signatures

docs/CHATWOOT_PARITY_DEVELOPMENT_PLAN.md

@@ -64,6 +64,7 @@ This ledger records the committed parity checkpoints that future slices should b
 | `66ecabb feat(webhook): persist provider receipt statuses` | Added delivery/read/failed status persistence for Twilio, WhatsApp, Facebook/Instagram, and TikTok receipt events. | Focused webhook/channel tests passed; full `go test ./...` passed. | Continue P6.7 review with async dispatch/events and broader provider fixture assertions. |
 | `06b999b feat(webhook): dispatch persisted provider events` | Wired webhook incoming persistence and status updates into the existing `channel.Dispatcher` fan-out boundary. | Focused webhook tests passed; full `go test ./...` passed. | Continue P6.7 review with broader provider fixture assertions. |
 | `55295dd test(webhook): cover provider ingress persistence fixtures` | Added provider-specific webhook persistence fixture assertions for LINE, Twilio SMS, WhatsApp, Instagram, and TikTok, extending the existing Telegram fixture. | Focused webhook tests passed; full `go test ./...` passed. | Continue P6.7 review with signature edge fixtures and final provider Done/Review classification. |
+| Working tree | Added Chatwoot-style TikTok `Tiktok-Signature` HMAC verification using `TIKTOK_APP_SECRET`, timestamp freshness, and invalid-signature rejection coverage. | Focused webhook tests passed; full `go test ./...` passed. | Continue P6.7 review with LINE/WhatsApp missing-signature edge fixtures and final provider classification. |
 
 ## Next Slice Contract
 
@@ -85,6 +86,7 @@ Current N1/N2 implementation checkpoint:
 - Added receipt persistence for status-only webhook events. Twilio delivery callbacks, WhatsApp statuses, Facebook/Instagram delivery/read receipts, and TikTok read receipts now update existing message statuses through the same boundary. Async event fan-out remains the next dispatch gap.
 - Wired the same boundary into `channel.Dispatcher` so incoming webhooks emit `contact.created`, `conversation.created/opened/updated`, `message.created/incoming`, and `message.status_updated` events for automation, CSAT, bot rules, notifications, and future async workers.
 - Added provider-specific persistence fixtures for Telegram, LINE, Twilio SMS, WhatsApp, Instagram, and TikTok. These tests assert durable `messages` rows by provider source ID instead of only checking webhook `200 OK` acknowledgements.
+- Added TikTok webhook signature verification to match `reference/chatwoot/app/controllers/webhooks/tiktok_controller.rb`: `Tiktok-Signature` must include `t=<unix>,s=<hmac>`, the HMAC is `sha256(TIKTOK_APP_SECRET, "<timestamp>.<raw_body>")`, and stale signatures older than five seconds are rejected.
 
 ## Immediate Execution Queue
 
@@ -513,7 +515,7 @@ Webhook ingress subtracking:
 | P6.7d | SMS/Twilio `POST /webhooks/sms/:phone_number` | `webhooks/sms#process_payload` | Go path was `/webhooks/twilio/sms/:phone_number`; handler read an inbox-style param. | Chatwoot path is registered, phone number resolves `ChannelTwilioSMS`, signature verification is applied where configured, and message/status events dispatch. | Review |
 | P6.7e | WhatsApp `GET/POST /webhooks/whatsapp/:phone_number` | `webhooks/whatsapp#verify`, `#process_payload` | Verify-token lookup scanned only account `0`, and Cloud signature verification used access token as a placeholder secret. | Verify challenge and POST event ingestion match Chatwoot path, token, response, and inbox resolution behavior. | Review |
 | P6.7f | Instagram `GET/POST /webhooks/instagram` | `webhooks/instagram#verify`, `#events` | Chatwoot no-param route was registered but still returned parity stub responses. | Verify/event routes exist at Chatwoot paths and resolve account/inbox from payload/subscription data. | Review |
-| P6.7g | TikTok `POST /webhooks/tiktok` | `webhooks/tiktok#events` | Go route expected `:business_id`; Chatwoot route has no path param and should derive identity from payload. | Handler accepts Chatwoot path, resolves business/inbox from payload, and acks/dispatches provider events. | Review |
+| P6.7g | TikTok `POST /webhooks/tiktok` | `webhooks/tiktok#events` | Go route expected `:business_id`; Chatwoot route has no path param and should derive identity from payload. | Handler accepts Chatwoot path, verifies `Tiktok-Signature`, resolves business/inbox from payload, and persists/dispatches provider events. | Done |
 | P6.7h | Shopify `POST /webhooks/shopify` | `webhooks/shopify#events` | Chatwoot route existed but returned parity stub responses. | Route either has a real verified handler or is explicitly tracked as unsupported without placeholder success. | Review |
 | P6.7i | Generic fallback and auth middleware | Go `WebhookAuth`, `webhookStub` | Generic middleware reads `:channel_type/:identifier`, which breaks provider-specific routes; fallback returned placeholder success. | Provider routes perform provider-specific verification; fallback no longer masks missing providers with success JSON. | Done |
 
@@ -606,3 +608,4 @@ Verification milestone gates:
 - 2026-06-04: Continued P6.7 dispatch parity by persisting provider receipt/status events. Existing messages are updated from Twilio delivery callbacks, WhatsApp sent/delivered/read/failed statuses, Facebook/Instagram delivery/read receipts, and TikTok read receipts. Added tests for direct status update and Twilio delivery callback update. Focused webhook/channel tests and full `go test ./...` passed.
 - 2026-06-05: Wired P6.7 incoming persistence into the existing dispatcher fan-out boundary. Newly persisted webhook contacts, conversations, messages, and message status updates now emit `ChannelEvent`s through `DispatchAsync`'s current sync fallback, keeping automation, bot rule, CSAT, and notification listeners reachable from provider webhooks. Added listener-based regression coverage for incoming and status events. Focused webhook tests and full `go test ./...` passed.
 - 2026-06-05: Broadened P6.7 provider webhook persistence fixtures. LINE, Twilio SMS, WhatsApp, Instagram, and TikTok webhook tests now assert persisted incoming `messages` by provider source ID, matching the existing Telegram persistence fixture and reducing the remaining provider-review surface to signature edge cases and final unsupported-provider classification. Focused webhook tests and full `go test ./...` passed.
+- 2026-06-05: Added TikTok webhook signature parity. `/webhooks/tiktok` now rejects missing, invalid, or stale `Tiktok-Signature` values using the same timestamp-plus-body HMAC shape as the Chatwoot reference controller, while valid signed payloads still resolve the inbox from `biz_id` and persist incoming messages. Focused webhook tests and full `go test ./...` passed.