Authenticate requests

Bearer, HMAC formats, and HS256 JWT #

Bearer mode expects Authorization: Bearer followed by the private token. Scheme casing is ignored; duplicate or ambiguous values are rejected. Authentication never falls through to another mode. Static-header presets for n8n, Make, and Zapier remain available.

HMAC mode signs the original request body bytes. Set hex or Base64 and the exact prefix, such as sha256=. Configure the header name explicitly. The GitHub documented format is X-Hub-Signature-256 with prefixed hex; Typeform documents Typeform-Signature with prefixed Base64. FlowRelay protocol fixtures cover these formats; they do not establish complete live sender compatibility. Check event fields, sender retries, and a real end-to-end test before adopting a named integration. Stripe's timestamped signature format is not supported by this generic verifier.

HS256 JWT is an advanced shared-secret mode. Configure the expected issuer and audience. Tokens must include expiry, issuer, and audience; not-before is checked when present. Clock tolerance is configured from zero to 60 seconds. Only HS256 is allowed; token-supplied key URLs and alternative algorithms are rejected. This is not OAuth or public-key JWT verification.

For sender-owned signing secrets, review a credential change in Endpoint setup and enter 32–512 UTF-8 bytes in the private confirmation form. Secrets are encrypted and omitted from exports. Generated credentials are revealed once. FlowRelay does not offer an unauthenticated endpoint mode.

• GitHub signature documentation
• Typeform signature documentation

Choose the authentication mode #

HMAC binds authentication to the exact body bytes and remains the stronger custom-code path. Static-header authentication is the compatible normal path for Zapier, Make, and n8n. Bearer and HS256 JWT are also available for senders that use those formats. Credentials can be generated in FlowRelay or supplied privately by the sender owner.

Request wire contract #

Send JSON with POST to the endpoint URL and put authentication in that endpoint's configured header. FlowRelay compares a static value exactly, verifies a Bearer token, checks configured HS256 JWT claims, or verifies HMAC-SHA256 over the exact raw request bytes. HMAC encoding and literal prefix must match the endpoint settings; the legacy default remains unprefixed hex. Parsing, reformatting, re-encoding, or otherwise changing the body after signing invalidates the HMAC signature.

body_bytes = utf8_encode(exact_json_body)
signature = lowercase_hex(hmac_sha256(FLOWRELAY_SIGNING_SECRET, body_bytes))
POST FLOWRELAY_ENDPOINT_URL
Content-Type: application/json
FLOWRELAY_CONFIGURED_AUTH_HEADER: signature
Body: body_bytes

curl -X POST "$FLOWRELAY_ENDPOINT_URL" \
  -H "Content-Type: application/json" \
  -H "$FLOWRELAY_CONFIGURED_AUTH_HEADER: $FLOWRELAY_STATIC_SECRET" \
  --data-binary '{"event_type":"synthetic.test","external_event_id":"synthetic-001"}'

Success check #

A test receipt shows that authentication passed before you enable production traffic. If authentication fails, fix the sender configuration and send a new test event with synthetic data.

Safe troubleshooting #

FLR_AUTH_HEADER_MISSING means the configured header name was absent. FLR_AUTH_FAILED means the configured static, Bearer, exact-body HMAC, or HS256 JWT credential did not verify. Two newest consecutive outside authentication failures within 30 minutes can prompt a guided, non-destructive replacement endpoint; the original remains active until you separately delete it. Correct the sender configuration and send a fresh event; do not replay an unauthenticated request. Share only the support code or a diagnostics share when someone needs help. Do not share the secret, full authentication header value, signature, raw event body, Shopify token, session data, or copied merchant incident.