# Device Management Implementation - Changelog

## Summary

Enhanced the auth service to properly support multi-device login with device management capabilities. **One phone number = One account**, but that account can be logged in from **multiple devices simultaneously**.

---

## Changes Made

### 1. Enhanced Verify OTP Endpoint (`/auth/verify-otp`)

**Added:**
- New device detection logic
- Audit logging for all login attempts
- Response fields: `is_new_device`, `is_new_account`, `active_devices_count`

**Response now includes:**
```json
{
  "user": { ... },
  "access_token": "...",
  "refresh_token": "...",
  "needs_profile": true,
  "is_new_device": false,          // NEW
  "is_new_account": false,         // NEW
  "active_devices_count": 2        // NEW
}
```

**Benefits:**
- Mobile app can show security notifications for new devices
- Track account creation vs. existing account login
- Display active device count in UI

---

### 2. Enhanced Refresh Token Endpoint (`/auth/refresh`)

**Added:**
- Updates `user_devices.last_seen_at` on token refresh
- Tracks device activity for monitoring

**Benefits:**
- Identify active vs. inactive devices
- Better device management insights

---

### 3. New User Endpoints (`/users/me/*`)

#### GET `/users/me`
- Returns user info with `active_devices_count`
- Includes account creation date and last login time

#### GET `/users/me/devices`
- Lists all active devices for the user
- Shows device metadata (platform, model, OS, etc.)
- Includes first_seen_at and last_seen_at timestamps

#### DELETE `/users/me/devices/:device_id`
- Revokes/logs out a specific device
- Revokes all refresh tokens for that device
- Logs the action in audit table

#### POST `/users/me/logout-all-other-devices`
- Logs out all devices except the current one
- Requires `current_device_id` in header or body
- Returns count of revoked devices

---

### 4. Audit Logging

**Added comprehensive logging:**
- Login attempts (success/failure)
- Device revocations
- Logout actions
- All events logged to `auth_audit` table with metadata

**Audit fields:**
- `action`: 'login', 'device_revoked', 'logout_all_other_devices'
- `status`: 'success', 'failed'
- `device_id`: Device identifier
- `ip_address`: Client IP
- `user_agent`: Client user agent
- `meta`: JSONB with additional context (is_new_device, platform, etc.)

---

## Database Changes

### No Schema Changes Required
- All features use existing tables:
  - `users` (already has UNIQUE constraint on phone_number)
  - `user_devices` (already tracks devices per user)
  - `auth_audit` (already exists for logging)
  - `refresh_tokens` (already tracks tokens per device)

### Existing Constraints Work Perfectly
- `phone_number UNIQUE` → One account per phone number ✅
- `(user_id, device_identifier) UNIQUE` → One device record per user-device combo ✅

---

## Security Improvements

### ✅ New Device Detection
- Automatically flags new device logins
- Mobile app can show security alerts
- Logged in audit table

### ✅ Device Activity Tracking
- `last_seen_at` updated on token refresh
- Helps identify abandoned devices
- Better security monitoring

### ✅ Device Management
- Users can see all active devices
- Users can revoke specific devices
- Users can logout all other devices (security feature)

### ✅ Audit Trail
- All authentication events logged
- Can track suspicious activity
- Compliance and security auditing

---

## API Usage Examples

### Login from New Device
```bash
POST /auth/verify-otp
{
  "phone_number": "+919876543210",
  "code": "123456",
  "device_id": "new-device-123",
  "device_info": { "platform": "android" }
}

Response:
{
  "is_new_device": true,
  "is_new_account": false,
  "active_devices_count": 2
}
```

### List Active Devices
```bash
GET /users/me/devices
Authorization: Bearer <access_token>

Response:
{
  "devices": [
    {
      "device_identifier": "device-1",
      "device_platform": "android",
      "last_seen_at": "2024-01-15T10:30:00Z",
      "is_active": true
    }
  ]
}
```

### Revoke Device
```bash
DELETE /users/me/devices/device-1
Authorization: Bearer <access_token>

Response:
{
  "ok": true,
  "message": "Device logged out successfully"
}
```

---

## Mobile App Integration

### New Response Fields to Handle

1. **`is_new_device`** → Show security notification
2. **`is_new_account`** → Show welcome flow
3. **`active_devices_count`** → Display in settings

### New Endpoints to Implement

1. **Device List Screen** → Show all active devices
2. **Revoke Device** → Allow users to logout specific devices
3. **Security Settings** → Show active device count

### Example Flow

```kotlin
// After login
if (response.is_new_device && !response.is_new_account) {
    showSecurityAlert("New device logged in: ${deviceModel}")
}

// In settings screen
val devices = apiClient.getDevices(accessToken)
devices.forEach { device ->
    showDeviceCard(
        model = device.device_model,
        lastSeen = device.last_seen_at,
        onRevoke = { revokeDevice(device.device_identifier) }
    )
}
```

---

## Testing Checklist

- [x] Same phone number can log in from multiple devices
- [x] Each device gets its own refresh token
- [x] Devices can be active simultaneously
- [x] Revoking one device doesn't affect others
- [x] New device detection works correctly
- [x] Audit logging captures all events
- [x] Device activity tracking works
- [x] Logout all other devices works

---

## Backward Compatibility

✅ **Fully backward compatible**
- All existing endpoints work as before
- New response fields are additions (optional to use)
- New endpoints are additions (don't break existing code)

---

## Next Steps

1. **Update Mobile App**
   - Handle new response fields
   - Implement device management UI
   - Show security notifications

2. **Monitoring**
   - Query `auth_audit` for suspicious activity
   - Monitor device counts per user
   - Alert on unusual patterns

3. **Future Enhancements**
   - Device name/labeling (let users name devices)
   - Push notifications on new device login
   - Device location tracking (optional)
   - Session limits (max devices per user)

---

## Files Modified

1. `src/routes/authRoutes.js` - Enhanced verify-otp and refresh endpoints
2. `src/routes/userRoutes.js` - Added device management endpoints
3. `DEVICE_MANAGEMENT.md` - New documentation
4. `CHANGELOG_DEVICE_MANAGEMENT.md` - This file

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## Questions?

See `DEVICE_MANAGEMENT.md` for detailed API documentation and examples.
