Webhook integration guide for SMS verification OTP
Polling activation status works for quick scripts, but production systems should react to events. SMSTwins webhooks push sms.received and lifecycle notifications to your HTTPS endpoint so backends parse verification OTP as soon as the gateway delivers the text. This guide teaches reliable integration — signature verification, idempotency, retries, and staging discipline — for engineering teams building onboarding tests or internal verification tools.
We cover setup, event payloads, HMAC-SHA256 validation, comparing webhooks versus polling, failure handling, and security baselines. Applies to inbound SMS text OTP via SMSTwins virtual numbers.
Why webhooks beat polling for OTP
Verification SMS often arrives within seconds. Polling adds latency, wastes rate limit budget, and complicates CI timing. Webhooks notify your server immediately when text lands.
Event-driven flows mirror production user experience more closely than sleep loops in tests.
Combine webhooks with POST /activations for full automation without dashboard copy-paste.
Configuring endpoints in SMSTwins
Register an HTTPS URL in your account webhook settings. SMSTwins provides a signing secret — store it in your secrets manager alongside API keys.
Use separate endpoints or secrets for staging and production to prevent test OTP leaking into live user databases.
Ensure your TLS certificate is valid and reachable from the public internet.
HMAC signature verification
Each request includes a signature header computed over the raw JSON body with HMAC-SHA256 using your webhook secret.
Compare signatures in constant time after computing expected HMAC on the untouched body — parsing JSON first can alter bytes and break validation.
Reject unsigned or mismatched requests before extracting OTP content.
Handling sms.received events
The payload identifies the activation and includes SMS body text. Parse OTP according to your target platform's format — regex for numeric codes is common but tune per service.
Make handlers idempotent: duplicate deliveries should not double-charge internal workflows or submit codes twice to external APIs.
Respond with 2xx quickly; offload heavy work to queues if needed so SMSTwins retries do not stack unnecessarily.
Lifecycle and timeout events
Listen for terminal states — success, cancellation, timeout — to release test workers and trigger automatic refund logic in your finance scripts.
Tests should fail clearly on timeout without blaming application code when infrastructure did not deliver SMS.
Correlate activation IDs across logs for debugging.
Staging and CI patterns
Expose staging endpoints via secure tunnels during local development; rotate tunnel URLs when secrets leak.
Gate live-SMS E2E tests in CI behind nightly jobs with cost alerts.
Start with sandbox API keys for wiring, then promote to live keys in controlled environments.
Production hardening checklist
HTTPS only, signature verification mandatory, secrets rotated, least-privilege API keys, minimal OTP retention in logs.
Monitor endpoint availability — prolonged outages may cause retry backlogs.
Read API Terms and Webhooks section in official docs for rate and retry specifics.
Webhook integration summary
SMSTwins webhooks deliver real-time SMS OTP events to your HTTPS endpoint. Verify HMAC-SHA256 signatures, handle sms.received idempotently, and track lifecycle timeouts for reliable automation.
Separate staging secrets, respond quickly with 2xx, and prefer events over polling for production-grade verification testing.
Webhook OTP FAQ
- Which algorithm signs webhooks?
- HMAC-SHA256 over the raw JSON body using your webhook secret, compared to the signature header documented in SMSTwins docs.
- Can I use HTTP not HTTPS?
- Production endpoints should use HTTPS with valid certificates. Plain HTTP is inappropriate for OTP delivery events.
- What if my endpoint is down?
- SMSTwins retries according to documented policy. Still monitor availability; OTPs remain visible in the dashboard as backup.
- Do webhooks include the full SMS text?
- Yes — sufficient to parse verification codes. Minimize retention in your logs.
- Can webhooks replace the REST API entirely?
- You still create activations via API or dashboard. Webhooks notify; they do not initiate sessions alone.