auth/JWT_SECURITY_AUDIT.md

JWT & Refresh Token Security Audit

Security Engineer Review

✅ SECURE IMPLEMENTATIONS

1. Token Storage (Android)

• Status: ✅ SECURE
• Implementation: Uses EncryptedSharedPreferences with AES256_GCM encryption
• Location: TokenManager.kt
• Details:
  • MasterKey with AES256_GCM scheme
  • PrefKeyEncryptionScheme: AES256_SIV
  • PrefValueEncryptionScheme: AES256_GCM
  • Tokens never stored in plain text
  • Tokens cleared on logout

2. Refresh Token Rotation

• Status: ✅ SECURE
• Implementation: Refresh tokens rotate on each refresh
• Location: tokenService.js - rotateRefreshToken()
• Details:
  • Old refresh token is revoked before issuing new one
  • New refresh token has new token_id (JTI)
  • Prevents token reuse attacks
  • Tracks rotation chain via rotated_from_id

3. Token Reuse Detection

• Status: ✅ SECURE
• Implementation: Detects and handles refresh token reuse
• Location: tokenService.js - handleReuse()
• Details:
  • If same refresh token used twice, all device tokens revoked
  • reuse_detected_at timestamp recorded
  • Prevents replay attacks

4. Token Versioning (Global Logout)

• Status: ✅ SECURE
• Implementation: Token version incremented on logout-all-devices
• Location: authMiddleware.js - validates token_version
• Details:
  • Each user has token_version in database
  • Tokens include token_version in payload
  • If version mismatch, token rejected
  • Allows global logout functionality

5. Idle Timeout

• Status: ✅ SECURE
• Implementation: Refresh tokens expire after 3 days of inactivity
• Location: tokenService.js - verifyRefreshToken()
• Details:
  • REFRESH_MAX_IDLE_MINUTES = 4320 (3 days)
  • Prevents long-lived abandoned sessions
  • Automatic cleanup of stale tokens

6. Device Binding

• Status: ✅ SECURE
• Implementation: Refresh tokens bound to device_id
• Location: tokenService.js - verifyRefreshToken()
• Details:
  • Token must match user_id AND device_id
  • Prevents token theft across devices
  • Device ID sanitized and validated

7. Token Hashing

• Status: ✅ SECURE
• Implementation: Refresh tokens hashed with bcrypt before storage
• Location: tokenService.js - storeRefreshToken()
• Details:
  • Tokens never stored in plain text in database
  • bcrypt.compare() used for verification
  • Even if database compromised, tokens not directly usable

8. JWT Claims Validation

• Status: ✅ SECURE
• Implementation: Validates JWT claims (iss, aud, exp, iat, nbf)
• Location: authMiddleware.js - validateTokenClaims()
• Details:
  • Prevents token manipulation
  • Ensures tokens are within valid time window
  • Validates issuer and audience

9. Access Token Short Lifetime

• Status: ✅ SECURE
• Implementation: Access tokens expire in 15 minutes
• Location: tokenService.js - signAccessToken()
• Details:
  • Limits exposure window if token stolen
  • Forces frequent refresh
  • Reduces impact of token leakage

⚠️ POTENTIAL ISSUES & RECOMMENDATIONS

1. Auto-Login on App Restart

• Status: ⚠️ FIXED
• Issue: User wasn't automatically logged in when reopening app
• Root Cause:
  • MainViewModel tried to validate tokens but didn't handle expired access tokens properly
  • Ktor's auto-refresh might not trigger on initial app startup
• Fix Applied:
  • Improved validateTokens() to try getUserDetails first (uses Ktor auto-refresh)
  • Falls back to manual refresh if auto-refresh doesn't work
  • Better error handling and token validation flow

2. Token Refresh on Startup

• Status: ✅ IMPROVED
• Implementation: Now properly handles token refresh on app startup
• Flow:
  1. Check if tokens exist
  2. Try to fetch user details (triggers Ktor auto-refresh if needed)
  3. If that fails, manually refresh token
  4. If refresh fails, clear tokens and logout

3. Network Error Handling

• Status: ✅ GOOD
• Implementation: Proper error handling for network failures
• Details:
  • Distinguishes between token expiration and network errors
  • Only clears tokens on authentication failures
  • Network errors don't force logout

🔒 SECURITY BEST PRACTICES FOLLOWED

1. ✅ Encrypted Storage: Tokens stored in EncryptedSharedPreferences
2. ✅ Token Rotation: Refresh tokens rotate on each use
3. ✅ Reuse Detection: Detects and prevents token reuse
4. ✅ Short Access Token Lifetime: 15 minutes
5. ✅ Idle Timeout: 3 days of inactivity
6. ✅ Device Binding: Tokens bound to specific device
7. ✅ Token Hashing: Refresh tokens hashed in database
8. ✅ Global Logout: Token versioning enables logout-all-devices
9. ✅ Claims Validation: JWT claims properly validated
10. ✅ Secure Transmission: Tokens sent in Authorization header (HTTPS required in production)

📋 RECOMMENDATIONS FOR PRODUCTION

1. HTTPS Enforcement:

   • Ensure all API calls use HTTPS
   • Implement certificate pinning for additional security

2. Token Expiration Monitoring:

   • Log token refresh events for security monitoring
   • Alert on suspicious refresh patterns

3. Rate Limiting:

   • Already implemented on backend
   • Monitor for abuse

4. Biometric Authentication (Future Enhancement):

   • Consider adding biometric unlock for sensitive operations
   • Store tokens behind biometric lock

5. Token Refresh Retry Logic:

   • Current implementation handles retries well
   • Consider exponential backoff for network failures

🎯 SUMMARY

Overall Security Rating: ✅ SECURE

The JWT and refresh token implementation follows security best practices:

• Secure storage (encrypted)
• Token rotation
• Reuse detection
• Short access token lifetime
• Device binding
• Global logout capability

Auto-Login Issue: ✅ FIXED

• Improved token validation flow
• Better handling of expired tokens on app startup
• Fallback mechanisms for token refresh

The implementation is production-ready from a security perspective. The main issue (auto-login) has been resolved.