# Token Refresh Mechanism

## Overview

The n8n integration includes automatic token refresh for both Zoho and Salesforce to ensure uninterrupted API access.

---

## How It Works

### Two-Level Token Refresh Strategy

#### 1. **Proactive Refresh** (Before Token Expires)
- Checks token expiration before every API call
- Refreshes token if it expires within **5 minutes**
- Prevents 401 errors before they happen

#### 2. **Reactive Refresh** (On 401 Error)
- If API returns 401 (Unauthorized), automatically refreshes token
- Retries the API call once with the new token
- Handles cases where token expired during the request

---

## Zoho Token Refresh

### Configuration Required

```env
ZOHO_CLIENT_ID=your_zoho_client_id
ZOHO_CLIENT_SECRET=your_zoho_client_secret
```

### Refresh Process

```javascript
// 1. Check if token is expired
const isExpired = expiresAt && new Date(expiresAt) <= new Date(Date.now() + 5 * 60 * 1000);

if (isExpired) {
  // 2. Call Zoho token refresh API
  POST https://accounts.zoho.com/oauth/v2/token
  Body:
    refresh_token: xxx
    client_id: xxx
    client_secret: xxx
    grant_type: refresh_token

  // 3. Receive new access token
  Response: {
    access_token: "new_token",
    expires_in: 3600
  }

  // 4. Update database with new token
  // 5. Use new token for API call
}
```

### Token Lifetime
- **Access Token**: 1 hour (3600 seconds)
- **Refresh Token**: Does not expire (unless revoked)
- **Proactive Refresh**: 5 minutes before expiry

---

## Salesforce Token Refresh

### Configuration Required

```env
SALESFORCE_CLIENT_ID=your_salesforce_client_id
SALESFORCE_CLIENT_SECRET=your_salesforce_client_secret
SALESFORCE_INSTANCE_URL=https://login.salesforce.com  # or https://test.salesforce.com for sandbox
```

### Refresh Process

```javascript
// 1. Check if token is expired
const isExpired = expiresAt && new Date(expiresAt) <= new Date(Date.now() + 5 * 60 * 1000);

if (isExpired) {
  // 2. Call Salesforce token refresh API
  POST https://login.salesforce.com/services/oauth2/token
  Body:
    grant_type: refresh_token
    refresh_token: xxx
    client_id: xxx
    client_secret: xxx

  // 3. Receive new access token
  Response: {
    access_token: "new_token",
    instance_url: "https://yourinstance.salesforce.com"
  }

  // 4. Update database with new token and instance URL
  // 5. Use new token for API call
}
```

### Token Lifetime
- **Access Token**: 2 hours (estimated, Salesforce doesn't return expires_in on refresh)
- **Refresh Token**: Does not expire (unless revoked or password changed)
- **Proactive Refresh**: 5 minutes before expiry

---

## Implementation Details

### File: `src/integrations/n8n/handler.js`

#### 1. Get Service Tokens
```javascript
async getServiceTokens(serviceName) {
  const tokenData = await userAuthTokenRepo.findByUserAndService(this.userId, serviceName);
  
  return {
    accessToken: decrypt(tokenData.accessToken),
    refreshToken: decrypt(tokenData.refreshToken),
    instanceUrl: tokenData.instanceUrl,
    expiresAt: tokenData.expiresAt  // ← Used to check expiration
  };
}
```

#### 2. Refresh Zoho Token
```javascript
async refreshZohoToken() {
  const { refreshToken } = await this.getServiceTokens('zoho');
  
  // Call Zoho refresh API
  const response = await axios.post('https://accounts.zoho.com/oauth/v2/token', params);
  const { access_token, expires_in } = response.data;
  
  // Update database
  await userAuthTokenRepo.upsertToken({
    userUuid: this.userId,
    serviceName: 'zoho',
    accessToken: encrypt(access_token),
    refreshToken: encrypt(refreshToken),
    expiresAt: new Date(Date.now() + expires_in * 1000)
  });
  
  return access_token;
}
```

#### 3. Refresh Salesforce Token
```javascript
async refreshSalesforceToken() {
  const { refreshToken, instanceUrl } = await this.getServiceTokens('salesforce');
  
  // Call Salesforce refresh API
  const response = await axios.post(`${tokenUrl}/services/oauth2/token`, params);
  const { access_token, instance_url } = response.data;
  
  // Update database
  await userAuthTokenRepo.upsertToken({
    userUuid: this.userId,
    serviceName: 'salesforce',
    accessToken: encrypt(access_token),
    refreshToken: encrypt(refreshToken),
    instanceUrl: instance_url || instanceUrl,
    expiresAt: new Date(Date.now() + 2 * 60 * 60 * 1000)  // 2 hours
  });
  
  return access_token;
}
```

#### 4. Fetch with Auto-Refresh
```javascript
async fetchZohoData(service, module, options) {
  try {
    let { accessToken, expiresAt } = await this.getServiceTokens('zoho');
    
    // Proactive refresh (check expiration)
    const isExpired = expiresAt && new Date(expiresAt) <= new Date(Date.now() + 5 * 60 * 1000);
    if (isExpired) {
      logger.info('Token expired, refreshing');
      accessToken = await this.refreshZohoToken();
    }
    
    // Make API call
    const result = await this.client.fetchZohoData(service, module, accessToken, query);
    return this.normalizeResponse(result, 'zoho');
    
  } catch (error) {
    // Reactive refresh (on 401 error)
    if (error.message.includes('401')) {
      logger.info('Received 401, refreshing token');
      const newAccessToken = await this.refreshZohoToken();
      const result = await this.client.fetchZohoData(service, module, newAccessToken, query);
      return this.normalizeResponse(result, 'zoho');
    }
    throw error;
  }
}
```

---

## Flow Diagram

### Successful Request (Token Valid)
```
User Request
    ↓
Check Token Expiration
    ↓
Token Valid (> 5 min remaining)
    ↓
Fetch Data from n8n
    ↓
Return Data to User
```

### Proactive Refresh (Token Expiring Soon)
```
User Request
    ↓
Check Token Expiration
    ↓
Token Expiring (< 5 min remaining)
    ↓
Refresh Token
    ↓
Update Database
    ↓
Fetch Data with New Token
    ↓
Return Data to User
```

### Reactive Refresh (401 Error)
```
User Request
    ↓
Check Token Expiration
    ↓
Token Appears Valid
    ↓
Fetch Data from n8n
    ↓
Receive 401 Error
    ↓
Refresh Token
    ↓
Update Database
    ↓
Retry Fetch Data
    ↓
Return Data to User
```

---

## Database Schema

### user_auth_tokens Table

```sql
CREATE TABLE user_auth_tokens (
  id INT PRIMARY KEY,
  user_uuid CHAR(36),
  service_name ENUM('zoho', 'salesforce', ...),
  access_token TEXT,      -- Encrypted
  refresh_token TEXT,     -- Encrypted (used for refresh)
  instance_url VARCHAR(255),  -- Salesforce only
  expires_at DATETIME,    -- Used to check if refresh needed
  created_at DATETIME,
  updated_at DATETIME
);
```

---

## Logging

### Token Refresh Logs

```
// Before refresh
INFO: Zoho token expired or expiring soon, refreshing { userId: 'xxx' }
INFO: Refreshing Zoho token { userId: 'xxx' }

// After successful refresh
INFO: Zoho token refreshed successfully { userId: 'xxx' }

// On 401 error
INFO: Received 401 error, attempting token refresh { userId: 'xxx' }
INFO: Refreshing Zoho token { userId: 'xxx' }
INFO: Zoho token refreshed successfully { userId: 'xxx' }

// On failure
ERROR: Failed to refresh Zoho token { userId: 'xxx', error: '...' }
```

---

## Error Handling

### No Refresh Token Available

```javascript
if (!refreshToken) {
  throw new Error('No Zoho refresh token available. Please re-authenticate.');
}
```

**User Action Required**: Re-authenticate via OAuth

### Refresh Token Expired/Revoked

```javascript
catch (error) {
  throw new Error(`Zoho token refresh failed: ${error.message}`);
}
```

**Possible Causes**:
- User revoked access
- Refresh token expired (rare)
- OAuth app credentials changed
- Password changed (Salesforce)

**User Action Required**: Re-authenticate via OAuth

---

## Best Practices

### 1. **5-Minute Buffer**
- Refreshes 5 minutes before expiry
- Prevents race conditions
- Accounts for clock skew

### 2. **Single Retry**
- Only retries once after token refresh
- Prevents infinite loops
- Fails fast if refresh doesn't work

### 3. **Encrypted Storage**
- All tokens encrypted in database
- Refresh tokens never logged
- Secure token transmission

### 4. **Database Updates**
- Updates `expires_at` after each refresh
- Keeps refresh token unchanged
- Updates instance URL (Salesforce)

---

## Testing Token Refresh

### Test Expired Token

```javascript
// Manually expire token in database
UPDATE user_auth_tokens 
SET expires_at = NOW() 
WHERE user_uuid = 'your-user-id' AND service_name = 'zoho';

// Make API call - should auto-refresh
curl -X GET "http://localhost:3000/api/v1/n8n/zoho/crm/leads" \
  -H "Authorization: Bearer YOUR_JWT"
```

**Expected Logs**:
```
INFO: Zoho token expired or expiring soon, refreshing
INFO: Refreshing Zoho token
INFO: Zoho token refreshed successfully
INFO: Fetching Zoho data via n8n
```

### Test 401 Error Handling

```javascript
// Use invalid token
UPDATE user_auth_tokens 
SET access_token = 'invalid_encrypted_token' 
WHERE user_uuid = 'your-user-id' AND service_name = 'salesforce';

// Make API call - should catch 401 and refresh
curl -X GET "http://localhost:3000/api/v1/n8n/salesforce/crm/leads" \
  -H "Authorization: Bearer YOUR_JWT"
```

**Expected Logs**:
```
INFO: Fetching Salesforce data via n8n
ERROR: n8n webhook call failed (401)
INFO: Received 401 error, attempting token refresh
INFO: Refreshing Salesforce token
INFO: Salesforce token refreshed successfully
INFO: Fetching Salesforce data via n8n (retry)
```

---

## Troubleshooting

### Issue: "No refresh token available"

**Cause**: User authenticated without requesting refresh token

**Solution**: 
1. Check OAuth scope includes refresh token
2. Re-authenticate user via `/oauth/callback`

### Issue: "Token refresh failed"

**Cause**: Refresh token invalid or expired

**Solution**:
1. User must re-authenticate
2. Check OAuth app credentials in `.env`

### Issue: Token refreshes but still gets 401

**Cause**: API issue or wrong credentials

**Solution**:
1. Check provider API status
2. Verify OAuth app has correct permissions
3. Check instance URL (Salesforce)

---

**Last Updated**: October 9, 2025  
**Version**: 1.0.0