Why Phone OTP Is Essential in the Indian Market
In India, email-based password authentication creates massive friction. Users forget complex passwords, and email verification links end up in spam folders. Mobile OTP (One-Time Password) delivers instant, high-converting onboarding.
However, a naive OTP implementation is vulnerable to SMS flooding attacks, brute-force guessing, and token leakage.
The 4 Security Rules for OTP Verification:
Hash the OTP using bcrypt or SHA-256 with a secret salt before storing it in Redis or PostgreSQL. When the user submits their code, hash their input and compare hashes in constant time to prevent timing attacks.
Upon successful verification, never store your JWT in browser localStorage where it is vulnerable to Cross-Site Scripting (XSS). Store it in a secure, SameSite=Strict, HttpOnly cookie that JavaScript cannot access.