OTP Login Sequence Diagram

Sequence diagram of phone number login with a one-time password: OTP generation, SMS delivery, verification and issuing a session token.

OTP Login Sequence Diagram — Sequence diagram

How it flows

  1. User → Server: POST /auth/request-otp (phone number)
  2. Server → Server: Generate OTP & set expiry
  3. Server → Database: Store OTP + expiry timestamp for phone number
  4. Database → Server: OTP record saved
  5. Server → SMS Gateway: Send OTP SMS to phone number
  6. SMS Gateway → User: SMS: Your OTP is XXXXXX
  7. Server → User: 200 OK (OTP sent)
  8. User → Server: POST /auth/verify-otp (phone number + OTP)
  9. Server → Database: Fetch stored OTP & expiry for phone number
  10. Database → Server: Return OTP record
  11. Server → Server: Verify OTP match & check not expired
  12. Server → Server: Generate signed JWT session token
  13. Server → Database: Invalidate / delete used OTP
  14. Database → Server: OTP invalidated
  15. Server → User: 200 OK (JWT session token)

Components

User · Server · Database · SMS Gateway

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