OTP sign-in needs clear delivery, expiry, resend and verification states, with controls enforced on the server. A message being dispatched does not prove the user received it. Design the failure and recovery journey without exposing whether an unrelated account exists or encouraging repeated code requests.
Let’s plan your OTP sign-in flow.
Bring your workflow, constraints and open questions. We’ll help you define the requirements and work through a practical next step.
Choose the authentication scope deliberately
Have the security owner select the authentication method appropriate to the product and its risks. SMS or email codes are not interchangeable with every stronger authentication method, and possession of a contact channel should not automatically merge existing accounts.
OWASP's authentication guidance addresses generic error responses, automated-attack controls and account recovery. Apply the relevant controls through the identity provider and application, not merely the visible countdown.
Specify the code lifecycle
| Event | User explanation | Server-side rule to agree |
|---|---|---|
| Request accepted | Where the code is expected | Eligibility and rate controls |
| Delivery delayed | Useful waiting and correction options | Provider failure handling |
| Resend requested | Which code remains valid | Invalidation and resend policy |
| Incorrect code | Clear recoverable error | Attempt limits and monitoring |
| Code expired | Request a valid new attempt | Authoritative expiry check |
| Contact unavailable | Approved recovery route | Identity verification process |
Do not invent a universal code duration or attempt count. Select and document values through the approved security design and provider capabilities.
Avoid a confusing resend race
For a hypothetical customer app, a user may request a second code just before the first arrives. Explain which attempt they should use and enforce the same rule consistently. Client clocks should not determine whether a code is valid.
Support correction of a mistyped contact destination without carrying an earlier code into the new identity context. Do not expose codes in analytics, screenshots generated for support or general logs.
Test assistive and interrupted entry
Verify paste, autofill where supported, keyboard interaction and readable errors. Multiple visual boxes should not make entering a code unnecessarily difficult.
Test app switching, connectivity loss and a provider outage. A failed verification request must not be presented as an incorrect code if the server never completed the check.
OTP questions
Does a countdown enforce expiry?
No. It communicates timing; the server or trusted identity service must enforce the actual rule.
Should support simply change the contact number on request?
Use the approved recovery and verification process. A convenient support shortcut can undermine the sign-in boundary.
Connect sign-in to session recovery, and discuss the flow with Drema's mobile team.
This article explains what to build, not legal advice. Rules change; confirm against the current official text before relying on it.
