feat: implement email verification on user registration (#40)

[Sendi0011]

🚀 feat: Implement Email Verification on User Registration

Closes #40

📋 Summary

This PR implements a comprehensive email verification system for user registration. When admins create new users through the CreateUserModal, the system automatically sends a verification email with a 6-digit OTP code. Users must verify their email address before their account becomes fully active.

✨ Key Features

🔐 Security-First Implementation

• SHA-256 Code Hashing: Verification codes are never stored in plain text
• Rate Limiting: Maximum 1 verification email per hour per user
• Attempt Limiting: Maximum 5 verification attempts before requiring a new code
• Time-Based Expiration: Codes expire after 5 hours for security
• Comprehensive Input Validation: All user inputs are thoroughly validated

📧 Professional Email Experience

• Branded HTML Templates: Beautiful, responsive emails matching Devote's yellow branding
• Clear Instructions: User-friendly verification process with visual code display
• Mobile Optimized: Email templates work perfectly on all devices
• Security Warnings: Clear messaging about code confidentiality and expiration

🎯 Seamless User Experience

• 3-Step Modal Flow: Create → Verify → Success with visual progress
• Real-time Feedback: Live attempt counters and expiration timers
• Smart Error Handling: Context-aware error messages with actionable guidance
• Resend Functionality: Users can request new codes with built-in cooldowns
• Visual Success Indicators: Clear confirmation when verification completes

🛠️ Technical Implementation

New Files Created

lib/verification.ts                              # Verification utilities and email templates
app/api/auth/send-verification/route.ts        # Send verification email endpoint
app/api/auth/verify-email/route.ts             # Code verification endpoint  
app/api/auth/check-verification-status/route.ts # Status checking endpoint
app/verify-email/page.tsx                      # Standalone verification page

Files Updated

models/user.ts                    # Added email verification fields
app/api/users/route.ts           # Updated user creation to send verification emails
components/CreateUserModal.tsx   # Enhanced with 3-step verification flow

Database Schema Changes

Added new fields to User model:

• isEmailVerified: boolean - Tracks verification status
• emailVerificationCode: string - Stores hashed verification code
• emailVerificationExpires: Date - Code expiration timestamp
• emailVerificationAttempts: number - Failed attempt counter
• lastVerificationEmailSent: Date - Rate limiting timestamp

🔄 User Flow

1. Admin Action: Admin creates user in CreateUserModal with email and INE
2. System Response: User account created, verification email automatically sent
3. User Receives: Professional email with 6-digit verification code
4. Verification: User enters code in modal or standalone page
5. Validation: System validates code with security checks
6. Completion: Account marked as verified, success confirmation shown

🧪 Testing Coverage

Happy Path Testing

• ✅ User creation triggers verification email
• ✅ Correct code verification succeeds
• ✅ Account status updates properly
• ✅ Success messages display correctly

Error Handling Testing

• ✅ Invalid codes show appropriate errors
• ✅ Expired codes trigger renewal prompts
• ✅ Rate limiting prevents email spam
• ✅ Attempt limits enforce security
• ✅ Network errors handled gracefully

Edge Cases

• ✅ Already verified users handled properly
• ✅ Non-existent users return appropriate errors
• ✅ Malformed requests rejected with clear messages

🚨 Breaking Changes

• User Creation Flow: Admins now see verification step after creating users
• Database Migration Required: Existing users need new verification fields
• Email Templates: New verification emails replace old account creation emails

🔧 Environment Requirements

Ensure these environment variables are configured:

EMAIL_SMTP_HOST=smtp.gmail.com
EMAIL_SMTP_PORT=587
EMAIL_SMTP_SECURE=false
EMAIL_USER=your-email@gmail.com
EMAIL_PASS=your-app-password
FRONTEND_URL=https://your-domain.com

📊 Performance Considerations

• Database Indexing: Added indexes for faster verification lookups
• Rate Limiting: Prevents system abuse and email service overload
• Efficient Hashing: SHA-256 provides security without performance impact
• Optimized Queries: Minimal database calls for better response times

🛡️ Security Measures

Security Feature	Implementation
Code Storage	SHA-256 hashed, never plain text
Rate Limiting	1 email per hour per user
Attempt Limits	5 tries before requiring new code
Time Expiration	5-hour code validity window
Input Validation	Comprehensive sanitization
Error Messages	Security-conscious, no information leakage

📋 Acceptance Criteria Met

✅ Users receive verification email upon registration
✅ Must enter correct verification code to complete registration
✅ Invalid or expired codes trigger appropriate error messages
✅ Emails sent using reliable provider with security best practices
✅ Rate limiting prevents abuse
✅ Verification codes encrypted in database
✅ Resend functionality with cooldown implemented
✅ Well-formatted professional emails
✅ User-friendly error messaging

🎯 Quality Assurance

• TypeScript: Full type safety throughout implementation
• Error Handling: Comprehensive error boundaries and user feedback
• Code Organization: Clean separation of concerns with utility classes
• Documentation: Detailed inline comments and function documentation
• Best Practices: Follows Next.js and React patterns consistently

🚀 Deployment Notes

1. Database Migration: Run migration to add verification fields to existing users
2. Environment Setup: Configure email service environment variables
3. Email Testing: Verify email delivery in staging environment
4. Rate Limit Monitoring: Monitor email sending rates post-deployment

📞 Support & Maintenance

• Logging: Comprehensive error logging for debugging
• Monitoring: Track verification success rates and common failures
• Analytics: User verification completion metrics
• Documentation: Complete implementation guide provided

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This implementation provides enterprise-grade email verification with security, usability, and maintainability at its core. Ready for production deployment! 🎉

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