Operations BroadNet answer

How do I build an OTP verification flow?

Last reviewed July 22, 20261 min readReviewed by BroadNet engineering

Quick answer

Build an OTP flow in five steps: generate a short single-use code server-side, send it over a high-priority channel with a fallback, store a hashed copy with a short expiry, verify the user's input against it with attempt limits, and rate-limit requests to defend against pumping. Keep the code out of logs, never trust the client to validate, and prefer network-based verification where it removes the code entirely.

Plain-language definitionVendor-neutralReviewed July 22, 2026

DiagramThe OTP journey, with channel fallback

User requests a codeSign-in, payment or sign-up
Your app calls the verify APIOne request per code
BroadNet delivers the codeOn the best available channelFallback if undeliveredSMSWhatsAppVoice
User enters the codeChecked against the issued code
VerifiedAccess granted

The long answer

Everything worth knowing, nothing that isn't.

§01

Generate and store securely

Create a 4–8 digit code server-side, store only a hash of it with a short TTL (5–10 minutes), and bind it to the user and channel. Never send the code to the client for comparison — verify on the server. See /answers/what-is-otp.

§02

Send with a fallback

Deliver over a direct, high-priority route and configure a fallback channel (flash call, WhatsApp, or voice) so a delayed SMS does not block the user. See /answers/best-channel-for-otp and /answers/sms-fallback-strategy.

§03

Verify with limits

Check the user's input against the stored hash, cap attempts before forcing a resend, invalidate on success, and expire quickly. See /answers/sms-otp-best-practices.

§04

Rate-limit and monitor

Limit requests per number and per IP to resist SMS pumping, and watch for spikes to unusual destinations. Consider silent network authentication to avoid sending a billable code at all. See /answers/what-is-sms-pumping and /answers/what-is-silent-network-auth.

BNWritten by the BroadNet engineering team·Operating carrier-grade messaging since 2003, headquartered in Dubai·Editorial standards

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Topic hubOTP verification explained

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