Supabase Webhooks Skill

When to Use This Skill

• How do I receive Supabase Database Webhooks (INSERT / UPDATE / DELETE)?
• How do I verify a Supabase Auth Hook signature?
• Why is my Supabase webhook-signature verification failing?
• How do I secure a Supabase Database Webhook when there is no signature?
• How do I implement a send_email / send_sms / custom_access_token Auth Hook?
• What does the v1,whsec_ secret prefix mean?

Two Surfaces, Two Security Models

Supabase sends outbound HTTP from two different systems. They do not share a security model — do not apply one's verification to the other.

Supabase documents no source-IP allowlist and no user-agent value for either surface. Do not build either into your receiver.

Verification (core)

Auth Hooks — Standard Webhooks HMAC-SHA256

const { Webhook } = require('standardwebhooks');

// Secret is issued as "v1,whsec_<base64>". Strip the "v1,whsec_" prefix; the
// remainder is STANDARD base64 that the library base64-DECODES to the raw HMAC
// key. Using the base64 string itself as the key rejects every real delivery.
const wh = new Webhook(process.env.SUPABASE_AUTH_HOOK_SECRET.replace('v1,whsec_', ''));

// Signs `{webhook-id}.{webhook-timestamp}.{raw_body}` and base64-compares in
// constant time against every space-delimited `v1,<sig>` entry, with a
// ±5-minute timestamp tolerance. Pass the RAW body — re-serialised JSON fails.
const payload = wh.verify(rawBody, {
  'webhook-id': headers['webhook-id'],
  'webhook-timestamp': headers['webhook-timestamp'],
  'webhook-signature': headers['webhook-signature'],
}); // throws WebhookVerificationError on failure

Database Webhooks — developer-configured shared secret

There is no signature to verify. Authenticate with a header you set yourself when creating the webhook, compared in constant time:

const crypto = require('crypto');

function timingSafeEqualStr(a, b) {
  const x = Buffer.from(a || '', 'utf8');
  const y = Buffer.from(b || '', 'utf8');
  if (x.length !== y.length) return false; // length is not secret here
  return crypto.timingSafeEqual(x, y);
}

// Header value comes from the headers JSON you pass to supabase_functions.http_request
function authenticateDatabaseWebhook(headers, secret) {
  if (!secret) return false;
  const authorization = headers['authorization'] || '';
  const presented = authorization.toLowerCase().startsWith('bearer ')
    ? authorization.slice(7).trim()
    : headers['x-webhook-secret'] || '';
  return timingSafeEqualStr(presented, secret);
}

if (!authenticateDatabaseWebhook(req.headers, process.env.SUPABASE_WEBHOOK_SECRET)) {
  return res.status(401).json({ error: 'Unauthorized' });
}

For complete handlers with tests, see examples/express/, examples/nextjs/, examples/fastapi/.

Database Webhook Events

Only three, all fired after the row change:

type is UPPERCASE and is the discriminator. The full payload has exactly four other top-level fields — there are no others:

{ "type": "INSERT", "table": "<table name>", "schema": "<schema name>", "record": { }, "old_record": null }

record / old_record mirror the table's own columns, so their inner shape is whatever your table defines.

Create one in the Dashboard (Integrations → Webhooks) or in SQL:

create trigger "my_webhook" after insert on "public"."my_table"
for each row execute function "supabase_functions"."http_request"(
  'https://example.com/webhooks/supabase',  -- url
  'POST',                                   -- method (POST or GET)
  '{"Content-Type":"application/json","Authorization":"Bearer YOUR_SHARED_SECRET"}',
  '{}',                                     -- params
  '1000'                                    -- timeout in ms
);

There is no delivery id header and no documented retry policy — pg_net is fire-and-forget within timeout_ms. Delivery history lives in the database's net schema. Idempotency is your receiver's job: dedupe on a primary key inside record / old_record.

Auth Hooks

Six hooks, config keys exactly as documented:

Auth Hooks are request/response, not fire-and-forget. The auth flow blocks on your reply and your JSON body changes what Supabase does. Errors are any status >= 400; a 429 or 503 is retried up to three times with a two-second backoff only if you also send a non-empty retry-after header (e.g. retry-after: true), inside a 5-second total budget for the whole invocation. Keep the handler fast and push slow work out of band. Always send Content-Type: application/json; 204 is rejected by custom_access_token, mfa_verification_attempt and password_verification_attempt, and 400 / 403 are turned into a 500 returned to your application.

Auth Hooks can alternatively be configured as a Postgres function (pg-functions://postgres/<schema>/<fn>), in which case no HTTP request leaves the instance and none of the above applies. This skill covers the HTTP variant.

Environment Variables

# Auth Hooks — the secret Supabase issues, including the "v1,whsec_" prefix
SUPABASE_AUTH_HOOK_SECRET=v1,whsec_UkxKUzBrOWt2c1hHTDF3YjNVSHhOZmw3Y0dyNXlKRHE=

# Database Webhooks — a shared secret YOU choose and put in the trigger's
# headers JSON. Supabase does not generate or sign anything here.
SUPABASE_WEBHOOK_SECRET=a-long-random-string-you-generate

Supabase's own config key for a hook secret is plural (e.g. SEND_SMS_HOOK_SECRETS) because multiple pipe-delimited secrets are planned for rotation. The webhook-signature header is already a space-delimited list of v1,<sig> entries for exactly that reason — accept if any entry matches.

Local Development

--path replaces the forwarded request path, so run one tunnel per surface:

# No install, no account required — creates a guest account on first run

# Database Webhooks (Express/Next.js on 3000; use 8000 for FastAPI)
npx hookdeck-cli listen 3000 supabase --path /webhooks/supabase

# Auth Hooks — a separate source, because --path replaces the request path
npx hookdeck-cli listen 3000 supabase-auth-hook --path /webhooks/supabase/auth-hook

Paste the first tunnel URL into the Dashboard (Integrations → Webhooks) and the second as the Auth Hook URI (Authentication → Hooks). One tunnel for both would route Auth Hooks into the Database Webhook handler and get a 401.

Reference Materials

• references/overview.md - Both surfaces, events, payload shapes
• references/setup.md - Dashboard and SQL configuration, getting secrets
• references/verification.md - Signature verification details and gotchas