Handle webhooks

Webhooks let you skip the polling loop. Register an HTTPS endpoint, and FlowBeacon will POST you signed event payloads as soon as they happen.

When to use this

• You ship a production integration and want to scale beyond polling.
• You need to react to evaluation.complete in near-real-time.
• You run a multi-tenant integrator and don't want to drive every poll loop yourself.

Supported events (v1)

Event	Fires when	Payload
evaluation.complete	A batch evaluation transitions to complete.	{ event, evaluation_id, organization_id, scenarios[] }

Each scenarios[] entry carries the same violations[], module_summary[], evaluated_codes[], passing_count, failing_count fields as GET /scenarios/{id}/results.

Future events will be announced in the Changelog. A subscription only receives the events it opted into.

Step 1 — Register a subscription

POST /api/public/v1/webhooks
Authorization: Bearer fb_live_EXAMPLE_xxxxxxxxxxxxxxxxxxxx
X-FB-Signature: t=1714564800,v1=...
Content-Type: application/json

{
  "url": "https://hooks.example.com/flowbeacon",
  "events": ["evaluation.complete"],
  "description": "Production handler"
}

Response (200):

{
  "ok": true,
  "data": {
    "id": "sub_example_01HZY...",
    "url": "https://hooks.example.com/flowbeacon",
    "events": ["evaluation.complete"],
    "description": "Production handler",
    "is_active": true,
    "signing_secret": "whsec_EXAMPLE_abcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdef",
    "warning": "Store this signing_secret securely — it will not be shown again."
  },
  "meta": { "watermark": "wm_a1b2c3d4" }
}

signing_secret is shown once

Store it somewhere durable. If it leaks, call POST /webhooks/{id}/rotate-secret — the previous secret stops working immediately, with no grace period.

Step 2 — Verify deliveries

Every webhook POST from FlowBeacon carries:

Header	Example	Meaning
X-FB-Event	evaluation.complete	Event name. Check against the subscription's registered list.
X-FB-Signature	t=1714564800,v1=9f86...	Timestamp + an encrypted signature over {ts}.{raw_body}.
User-Agent	FlowBeacon-Webhook/1.0	Stable identifier.

Canonical signed string for webhooks:

message = "{timestamp}.{raw_request_body}"

Note: the webhook signature covers timestamp + body only (no method, no path). The receiver controls the URL, so signing it would be redundant. Tolerance window is 300 seconds.

The signing key is the subscription's signing_secret, not the API key.

TypeScript (Express)

import crypto from 'node:crypto';
import express from 'express';

const app = express();

// IMPORTANT: capture the raw body BEFORE any JSON middleware.
app.use(express.raw({type: 'application/json'}));

app.post('/flowbeacon', (req, res) => {
  const header = req.header('x-fb-signature') ?? '';
  const pairs = header
    .split(',')
    .map((p) => p.split('='))
    .filter((pair) => pair.length === 2);
  const parts = Object.fromEntries(pairs);
  const ts = Number(parts.t);
  if (!ts || Math.abs(Date.now() / 1000 - ts) > 300) {
    return res.status(403).end('stale or missing timestamp');
  }
  const expected = crypto
    .createHmac('sha256', process.env.FB_SIGNING_SECRET!)
    .update(`${ts}.${req.body.toString('utf8')}`)
    .digest('hex');
  const actualBuf = Buffer.from(parts.v1 ?? '', 'hex');
  const expectedBuf = Buffer.from(expected, 'hex');
  const ok =
    actualBuf.length === expectedBuf.length &&
    crypto.timingSafeEqual(actualBuf, expectedBuf);
  if (!ok) return res.status(403).end('bad signature');

  // ACK immediately. Process async.
  res.status(200).end();
  void process(JSON.parse(req.body.toString('utf8')));
});

Python (FastAPI)

import hashlib, hmac, os, time
from fastapi import FastAPI, Header, HTTPException, Request

app = FastAPI()

@app.post("/flowbeacon")
async def webhook(req: Request, x_fb_signature: str = Header(default="")):
    raw = await req.body()  # raw bytes — do not parse first
    try:
        parts = dict(p.split("=") for p in x_fb_signature.split(","))
        ts = int(parts["t"])
    except Exception:
        raise HTTPException(403, "bad header")
    if abs(time.time() - ts) > 300:
        raise HTTPException(403, "stale")
    expected = hmac.new(
        os.environ["FB_SIGNING_SECRET"].encode(),
        f"{ts}.{raw.decode()}".encode(),
        hashlib.sha256,
    ).hexdigest()
    if not hmac.compare_digest(parts.get("v1", ""), expected):
        raise HTTPException(403, "bad signature")
    # ACK now; process async.
    enqueue(raw)
    return {"ok": True}

Always verify on raw bytes

Verify the raw request body bytes, before any JSON parsing or middleware reformatting. JSON re-serialisation will change byte order, whitespace, or numeric formatting and break the signature.

Step 3 — Be idempotent

• At-least-once delivery. A 2xx response is taken as acknowledged. Brief duplicates are possible if the network confirms after timeout.
• No ordering guarantees across subscriptions or events.
• Use evaluation_id as your dedupe key. A simple in-memory LRU or a seen_events table works fine.

async function process(payload: {evaluation_id: string}) {
  if (await seen(payload.evaluation_id)) return;
  await markSeen(payload.evaluation_id);
  await doRealWork(payload);
}

Delivery semantics

Aspect	Behaviour
Retries	Up to 3 attempts per delivery with the same signed payload.
Per-attempt timeout	10 seconds.
Backoff	Built-in. Not configurable.
ACK	Any 2xx response ends the delivery.
Quarantine	None today. Operators monitor delivery_failure_count via GET /webhooks.

Operations

• GET /webhooks — list every subscription owned by the calling organization, including revoked ones. Returns last_delivery_at, last_delivery_status, delivery_failure_count.
• DELETE /webhooks/{id} — revoke immediately. No further deliveries fire.
• POST /webhooks/{id}/rotate-secret — returns a new signing_secret. The previous one stops working instantly. Reset delivery_failure_count to zero.

Local development

http:// URLs are accepted only for localhost, 127.0.0.1, and [::1]. Use a tunnel (e.g. ngrok, cloudflared) to expose your local handler to a public HTTPS URL while testing.