📲 OTP Authentication Flow in Java (Spring Boot)

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📲 OTP Authentication Flow in Java (Spring Boot) — Secure, Fast & Scalable in 5 Steps! 🔐🚀

Need to build a secure One-Time Password (OTP) login flow for your mobile or web app? Here's a clean and production-grade architecture to implement OTP authentication using Java, Spring Boot, Redis, and JWT — in just 5 key engineering steps. ⚙️



1️⃣ Generate & Send OTP

🎯 Goal: Create and send a time-bound OTP to the user’s mobile/email
🛠️ Tech Stack: Java (Spring Boot), Redis, Twilio or Email API
📍Use Case: User enters mobile/email → system sends 6-digit OTP
🔐 Security: OTP TTL is set in Redis (e.g., 5 minutes), retry limits are enforced
📝 Implementation Steps:
  • Generate a 6-digit numeric OTP.
  • Send OTP using Twilio (SMS) or Email API.
  • Store OTP with a unique Redis key tied to user identifier (e.g., OTP_user123).
  • Set TTL in Redis (typically 300 seconds).
  • Log the request and enforce basic spam protection (e.g., max 3 OTPs in 10 mins).




2️⃣ Store OTP Securely in Redis

🎯 Goal: Save OTP in Redis with automatic expiration to ensure security
🛠️ Tech Stack: Redis, Spring Boot, Spring Cache or RedisTemplate
📍Use Case: OTP stored with a key like OTP_userId and expires automatically
🧨 Prevent Abuse: Throttle OTP generation using Redis counters (e.g., otp_attempt_user123)
📝 Implementation Steps:
  • Use Redis to store the OTP against a key like OTP_user_abc.
  • Set expiration (e.g., 5 minutes) when setting the key.
  • Track the number of OTP generation requests using a separate Redis counter per user/IP.
  • Deny new OTPs if the user exceeds allowed limit (e.g., 5 OTPs per hour).




3️⃣ Verify OTP

🎯 Goal: Validate the OTP submitted by the user against Redis-stored value
🛠️ Tech Stack: Java (Spring Boot), Redis
📍Use Case: Compare user input vs stored OTP, allow only 3 attempts
✅ On Success: Delete the OTP key and create a login session or JWT
❌ On Failure: Increment attempt count in Redis and block after 3 wrong attempts
📝 Implementation Steps:
  • Retrieve the OTP from Redis using the key OTP_user_abc.
  • Compare the user’s submitted OTP with the stored one.
  • Track verification attempts using another Redis key.
  • Allow up to 3 attempts. On success, delete the OTP from Redis.
  • On repeated failure, temporarily block OTP verification for that user.




4️⃣ Session or JWT Token Generation

🎯 Goal: Issue a secure session or JWT token upon successful OTP verification
🛠️ Tech Stack: Java JWT (e.g., jjwt or auth0), Spring Security
📍Use Case: Once OTP is validated, generate token for further requests
🔒 Bonus: Attach userId, issuedAt, expiry, and roles to JWT payload
📝 Implementation Steps:
  • Use a JWT library to generate a signed token.
  • Include user ID, timestamp, and expiry (e.g., 15 mins) in the payload.
  • Return the token in the response header or body (typically as Bearer Token).
  • Use Spring Security to validate and authorize further API requests.




5️⃣ Audit & Rate-Limit Monitoring

🎯 Goal: Track OTP traffic and block suspicious or abusive behavior
🛠️ Tech Stack: Redis (rate-limiting), Spring AOP, ELK Stack (optional)
📍Use Case: Monitor OTP request and validation counts per user/IP
🚨 Real-time Alerts: Alert if OTP attempts or request rates exceed safe limits
📝 Implementation Steps:
  • Track OTP send and verify attempts using Redis per user/IP.
  • Implement Spring AOP to log all OTP-related actions.
  • Integrate with ELK or Prometheus/Grafana for alerting and dashboards.
  • Block IP or user account temporarily if thresholds are exceeded.




✅ Summary

This OTP architecture ensures:

  • ✅ Secure and time-limited OTPs
  • ✅ Scalable in-memory storage via Redis
  • ✅ Abuse protection with throttling and tracking
  • ✅ JWT-based stateless authentication
  • ✅ Auditable and observable with real-time alerts

Perfect for mobile logins, passwordless auth, and 2FA workflows! 🔐





📋 Want the Full Implementation?

Please download the full implementation document from the link below 👇👇👇

➡️ Click here to download the full OTP implementation 📄

Thanks for reading! 💬 Drop questions, thoughts, or suggestions in the comments!

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