Outbound webhooks

A Webhook Endpoint is a workspace-owned outbound event delivery target. The starter ships endpoint management, signed payloads, attempt history, retries, replay, test sends, and secret rotation via Cloudflare Queues.

The published event allowlist is api_token.created, api_token.revoked, webhook_endpoint.created, workspace_member.added, workspace_member.removed, workspace_member.role_changed, workspace_invitation.accepted, and billing.plan_changed. Each event has a dedicated payload shape and the publisher drops fields outside that shape; secrets, audit metadata, and actor provenance are never forwarded. The corresponding audit taxonomy is broader: events without a webhook allowlist entry remain audit-only. Membership-added delivery covers successful invitation acceptance; direct SSO provisioning and other Better Auth plugin writes are outside this capability seam. Fan out happens after the authoritative mutation and is best effort, so refused, duplicate, and no-op changes do not emit a domain webhook.

Endpoint lifecycle

• Created from the workspace webhooks UI, REST, or MCP
• Each endpoint has a URL, a signing secret, and a list of event types it subscribes to
• URLs are validated at creation and on every update (and re-checked at dispatch): https only, no embedded credentials, no localhost or single-label hostnames, and no private, loopback, or link-local IP literals. Invalid URLs fail with InvalidWebhookUrl (400). DNS-rebinding protection is out of scope for the starter.
• Disabling an endpoint stops delivery without losing history; updating it with enabled: true (PATCH) re-enables it
• Updating (PATCH) changes the URL, the event subscriptions, or the enabled flag (only the fields you send)
• Deleting an endpoint removes it and its delivery history (the deliveries cascade); rotation, updates, deletions, and replays all write Audit Events through WebhookEndpoints in @b2b-saas-starter/capabilities

Delivery

When a domain event matches an endpoint's subscriptions, the publisher queues one message for that endpoint. The background Worker signs and posts it with a 10-second request deadline, then reads at most a 2 KiB response prefix with a separate two-second body-read deadline. An unreadable or timed-out body is stored as absent; the HTTP status still determines delivery success or retry.

Each delivery has a summary and immutable individual attempt evidence. A later successful retry preserves earlier failures. The complete event payload stays on the summary for replay.

Each request body is {"deliveryId": "whd_…", "eventType": "…", "payload": …}. The producer assigns deliveryId before enqueueing. It is also the persisted summary ID and webhook-id, and stays unchanged across automatic retries and transfer to the dead-letter queue. A manual replay creates a new message ID and links its summary to the source through replayedFrom. The event type and payload stay unchanged, so receivers can distinguish a requested replay from a retry.

Requests follow Standard Webhooks, using the same signature format as Outpost's Standard Webhooks mode:

• webhook-id: the delivery ID
• webhook-timestamp: Unix seconds at signing time, refreshed for every attempt
• webhook-signature: space-separated v1,<base64> signatures, current key first
• x-trace-id: the trace ID you can quote in a support request

Signing secrets use whsec_<base64>, encoding 32 random bytes. Decode the base64 part to obtain the HMAC key. The signed bytes are the UTF-8 encoding of `${webhookId}.${timestamp}.${rawBody}`. The digest is HMAC-SHA256, encoded as standard base64. Verify the raw body before parsing JSON; reformatting changes the signature.

For a receiver, use the independent standardwebhooks package:

import { Webhook } from 'standardwebhooks'
 
export async function receive(request: Request, signingSecret: string) {
  const rawBody = await request.text()
  const event = new Webhook(signingSecret).verify(rawBody, {
    'webhook-id': request.headers.get('webhook-id') ?? '',
    'webhook-timestamp': request.headers.get('webhook-timestamp') ?? '',
    'webhook-signature': request.headers.get('webhook-signature') ?? ''
  })
  // Verification throws for invalid signatures or timestamps outside five minutes.
  // Atomically deduplicate webhook-id in your durable event handler before effects.
  return event
}

The verifier tries all signatures, so a receiver with either active key works during rotation. Deduplicate automatic retries on webhook-id; retain your processed IDs for at least your retry and operational recovery window. A manual replay deliberately has a new ID and can run your handler again.

Retries and delivery statuses

Delivery rows use one of five statuses: pending (an operator replay or test send created the row and the queue has not dispatched it yet), delivered (2xx), failed (retryable: 5xx, 408, 429, network error, or timeout), failed_permanent (non-retryable 4xx or an endpoint URL that fails the dispatch-time validation; acked, no retry), and dead_lettered (retries exhausted).

Retryable failures back off linearly: min(attempts, 6) × 30s (so 30, 60, 90 … up to 180s); the persisted nextAttemptAt is derived from the same formula. The QueueConsumer is configured with maxRetries = 6, batchSize = 25, maxConcurrency = 4, and retryDelay = 30s (see alchemy.run.ts and apps/background/wrangler.jsonc). On failure the worker calls message.retry({ delaySeconds }) and lets Cloudflare schedule the next attempt. After maxRetries, Cloudflare moves the message to the dead-letter queue b2b-saas-starter-webhooks-dlq, where a consumer on the same Worker marks the message's delivery row terminal (dead_lettered) and records a workspace Notification so members see the endpoint stopped receiving.

Operator tooling

The webhooks page and the REST surface share one operator toolkit:

• Deliveries drawer: per endpoint, newest first, with each attempt's evidence (payload, request headers, response status, truncated response body). GET /workspaces/:slug/webhooks/:endpointId/deliveries is the REST read (a read-scope token may list it; it is also the list_webhook_deliveries MCP tool).
• Replay: re-enqueues a failed delivery (failed, failed_permanent, or dead_lettered) verbatim: a new pending row with attempts reset to 0, carrying the original payload and a replayedFrom link to the source row, which is never modified. The replay writes a webhook.delivery_replayed Audit Event. REST: POST /workspaces/:slug/webhooks/deliveries/:deliveryId/replay. Anything on a disabled endpoint refuses with 409. Every delivery row records its payload (terminal rows included), so there is always a payload to resend.
• Test send: queues a synthetic webhook.test_event delivery to one enabled endpoint so an operator can prove a receiver's configuration end to end. REST: POST /workspaces/:slug/webhooks/:endpointId/test-event.
• Rotate secret: mints a new signing secret shown once. See below for the receiver contract. REST: POST /workspaces/:slug/webhooks/:endpointId/rotate-secret.

Attempt history and retention

Expand View attempt history in the deliveries drawer to load the timeline. Each HTTP attempt shows its ordinal, status, timestamp, duration, failure reason, request headers, and bounded response body when available. Terminal bookkeeping has no HTTP duration and preserves the last HTTP evidence on the summary.

REST exposes GET /workspaces/:slug/webhooks/deliveries/:deliveryId/attempts. The read-only MCP tool is list_webhook_delivery_attempts. Both require webhook:list and restrict results to the owning workspace.

The first stored observation wins. Duplicate and late observations cannot regress the summary or repeat streak changes and audits. Accepted failures update the endpoint's streak; success resets it. At 20 consecutive failures the endpoint is disabled atomically with the attempt and its audit. Terminal bookkeeping after an HTTP attempt does not count another failure or undo an operator's re-enable. Notifications are best-effort after persistence.

Network delivery remains at-least-once. A crash or concurrent processing can POST twice even though stored evidence is duplicate-safe. Receivers must deduplicate webhook-id durably.

The daily schedule deletes at most 100 summaries older than 30 days per pass, cascading their attempts. A large backlog takes multiple passes to drain. Digest delivery and history cleanup settle independently. Replay provenance keeps the source ID even after the source expires.

Secret rotation

Rotating an endpoint's secret starts a 24-hour grace window. During that window, the replaced secret signs deliveries alongside the new one.

For receivers this means:

1. During the grace window, webhook-signature carries two space-separated v1,<base64> entries: the first computed with the new secret, the second with the old one. A receiver still holding the old secret keeps verifying deliveries while its operator installs the new one. Verify against every entry.
2. Install the new secret as soon as you can (within 24 hours). After the window closes, deliveries are signed with the new secret only, and a receiver still on the old secret starts failing verification.
3. Rotating again inside the window drops the original secret entirely: only the last two secrets are ever active.
4. The new secret is displayed once at rotation (web UI and REST response); store it immediately.

Provider webhooks vs Webhook Endpoints

Stripe webhooks, GitHub webhooks, and other provider callbacks are integration-specific routes on the API or background Worker; they are inbound traffic. A Webhook Endpoint is the outbound surface a workspace uses to push events to its own systems. They are not the same concept.