# Better Auth Migration

## Overview
Migrated from NextAuth v5 (beta) to Better Auth for unified authentication across both Elysia (backend) and Next.js (frontend).

## Backend Changes

### Installation
- Added `better-auth@1.4.18` package
- Added `pg@8.18.0` for PostgreSQL connection pool

### New Files
- `backend/src/auth.ts` - Better Auth instance configuration
- `backend/src/routes/better-auth.ts` - Route handler for auth endpoints
- `backend/src/better-auth-migrate.ts` - Database migration script

### Modified Files
- `backend/src/index.ts` - Replaced custom auth routes with Better Auth routes
- Removed custom JWT-based authentication routes (`backend/src/routes/auth.ts` can be deleted after migration)

### Database Schema
New tables added:
- `session` - Session management
- `account` - OAuth/credential account storage
- `verification` - Email verification tokens

Existing `users` table extended with:
- `email_verified` (BOOLEAN)
- `image` (TEXT)

### Migration Steps
1. Run the migration script:
   ```bash
   cd backend
   bun run src/better-auth-migrate.ts
   ```

2. Set environment variables:
   ```env
   BETTER_AUTH_SECRET=<generate with: openssl rand -base64 32>
   BETTER_AUTH_URL=http://localhost:3001
   ```

## Frontend Changes

### Installation
- Added `better-auth` package (includes React client)

### New Files
- `frontend/lib/better-auth.ts` - Better Auth client instance

### Modified Files
- `frontend/lib/auth.ts` - Updated to use Better Auth session
- `frontend/app/auth/signin/page.tsx` - Updated to use Better Auth methods
- `frontend/app/auth/signup/page.tsx` - Updated to use Better Auth methods
- Removed `frontend/app/api/auth/[...nextauth]/route.ts` - No longer needed

### Authentication Methods
Better Auth supports:
- Email/password (`signIn.email`, `signUp.email`)
- OAuth providers (`signIn.social`):
  - GitHub (`signIn.social({ provider: 'github' })`)
  - Google (`signIn.social({ provider: 'google' })`)

### Session Management
```typescript
import { useSession } from '@/lib/better-auth';

// In client components
const { data: session } = useSession();
```

```typescript
import { authClient } from '@/lib/better-auth';

// In server components
const { data: session } = await authClient.getSession();
```

## Environment Variables

### Required
```env
# Backend
DATABASE_URL=postgres://user:password@localhost:5432/fiscal
BETTER_AUTH_SECRET=<32+ character random string>
BETTER_AUTH_URL=http://localhost:3001

# OAuth Providers
GITHUB_ID=<your github client id>
GITHUB_SECRET=<your github client secret>
GOOGLE_ID=<your google client id>
GOOGLE_SECRET=<your google client secret>

# Frontend
NEXT_PUBLIC_API_URL=http://localhost:3001
```

## API Endpoints

Better Auth provides these endpoints automatically (mounted at `/api/auth/*`):

### Email/Password
- `POST /api/auth/sign-up/email` - Sign up with email
- `POST /api/auth/sign-in/email` - Sign in with email
- `GET /api/auth/get-session` - Get current session
- `POST /api/auth/sign-out` - Sign out

### OAuth
- `GET /api/auth/sign-in/social` - Initiate OAuth flow
- `GET /api/auth/callback/*` - OAuth callback handler

### Session
- `GET /api/auth/get-session` - Get current session
- `POST /api/auth/update-session` - Update session data

## Key Differences from NextAuth

### NextAuth
- Configuration in route handler (`app/api/auth/[...nextauth]/route.ts`)
- Server-side session management with JWT
- Custom callback for session/user data
- Requires `signIn()` and `signOut()` from `next-auth/react`

### Better Auth
- Configuration in separate file (`backend/src/auth.ts`)
- Server and client components unified API
- Built-in session management with database storage
- `signIn.email`, `signIn.social`, `signOut` from `better-auth/react`
- Direct database access for user/session data

## Testing Checklist

- [ ] Run database migration: `bun run src/better-auth-migrate.ts`
- [ ] Start backend server
- [ ] Test email/password signup
- [ ] Test email/password login
- [ ] Test GitHub OAuth
- [ ] Test Google OAuth
- [ ] Test sign out
- [ ] Test protected routes redirect to sign in
- [ ] Test session persistence across page refreshes

## Rollback Plan

If issues arise, revert to NextAuth:
1. Restore `frontend/app/api/auth/[...nextauth]/route.ts`
2. Restore `frontend/app/auth/signin/page.tsx` and `frontend/app/auth/signup/page.tsx`
3. Restore `frontend/lib/auth.ts`
4. Remove `backend/src/auth.ts` and `backend/src/routes/better-auth.ts`
5. Restore custom auth routes in backend

## Benefits of Better Auth

1. **Unified Auth** - Single auth system for both backend and frontend
2. **Type Safety** - Better TypeScript support
3. **Database-Backed Sessions** - More secure than JWT
4. **Extensible** - Plugin system for 2FA, email verification, etc.
5. **Active Development** - More frequent updates and improvements
6. **Framework Agnostic** - Works with any backend framework

## Future Improvements

1. Enable email verification (Better Auth plugin)
2. Add two-factor authentication (Better Auth plugin)
3. Implement account management (password reset, email change)
4. Add session management UI (view active sessions, revoke)
5. Implement role-based access control (Better Auth plugin)

## Resources

- Better Auth Docs: https://www.better-auth.com/
- Better Auth GitHub: https://github.com/better-auth/better-auth
- Migration Guide: https://www.better-auth.com/docs/migration