Security Best Practices for User API

The OpenConnector User API implements comprehensive security measures to protect against various attack vectors including Cross-Site Scripting (XSS) attacks and brute force login attempts.

Overview

Our security implementation includes multiple layers of protection:

1. Input Validation & Sanitization
2. Rate Limiting & Brute Force Protection
3. Security Headers
4. Session Management
5. Logging & Monitoring

Protection Against Cross-Site Scripting (XSS)

Input Sanitization

All user inputs are automatically sanitized through our SecurityService:

// Automatic sanitization of all inputs
$sanitizedData = $this->securityService->sanitizeInput($data);

Features:

• HTML entity encoding to prevent script injection
• Removal of dangerous patterns (script tags, event handlers)
• Null byte filtering
• Length limiting to prevent DoS attacks

Security Headers

Every API response includes security headers:

• X-Frame-Options: DENY - Prevents clickjacking
• X-Content-Type-Options: nosniff - Prevents MIME sniffing
• X-XSS-Protection: 1; mode=block - Browser XSS protection
• Content-Security-Policy - Restricts resource loading
• Referrer-Policy - Controls referrer information

Content Validation

Login credentials undergo strict validation:

// Username validation
- Minimum 2 characters
- No dangerous characters (<, >, ', ', /, \)
- Maximum length limits
- Character encoding validation

// Password validation  
- Maximum length limits (prevents DoS)
- No HTML encoding (preserves actual password)

Protection Against Brute Force Attacks

Multi-Layer Rate Limiting

The system implements sophisticated rate limiting:

Per-User Rate Limiting

• Limit: 5 failed attempts per 15-minute window
• Action: Progressive delays then account lockout
• Duration: 1 hour lockout after threshold

Per-IP Rate Limiting

• Limit: 5 failed attempts per 15-minute window
• Action: IP address blocking
• Duration: 1 hour lockout after threshold

Progressive Delays

• Base Delay: 2 seconds
• Escalation: Exponential backoff (2s → 4s → 8s → 16s → 32s → 60s max)
• Reset: Successful login clears delays

Account Lockout Protection

// Automatic lockout triggers
if ($userAttempts >= 5) {
    // Lock account for 1 hour
    $lockoutUntil = time() + 3600;
    $this->cache->set($userLockoutKey, $lockoutUntil, 3600);
}

IP-based Protection

• Tracks failed attempts per IP address
• Blocks suspicious IP addresses automatically
• Considers proxy headers (X-Forwarded-For, etc.)
• Validates IP formats to prevent spoofing

Security Event Logging

All security events are logged with contextual information:

Logged Events

• failed_login_attempt - Invalid credentials
• rate_limit_exceeded - Too many attempts
• user_locked_out - Account temporarily disabled
• ip_locked_out - IP address blocked
• successful_login - Authentication succeeded
• login_attempt_during_lockout - Attempt during lockout period

Log Information

{
    'event': 'failed_login_attempt',
    'username': 'sanitized_username',
    'ip_address': '192.168.1.1',
    'reason': 'invalid_credentials',
    'user_attempts': 3,
    'ip_attempts': 2,
    'timestamp': '2024-01-15 14:30:22'
}

Implementation Details

SecurityService Features

The SecurityService class provides:

// Rate limiting check
$rateLimitCheck = $this->securityService->checkLoginRateLimit($username, $clientIp);

// Input sanitization
$sanitizedInput = $this->securityService->sanitizeInput($input);

// Credential validation
$validation = $this->securityService->validateLoginCredentials($credentials);

// Security headers
$response = $this->securityService->addSecurityHeaders($response);

// IP address detection
$clientIp = $this->securityService->getClientIpAddress($request);

Cache-based Storage

Security data is stored using NextCloud's distributed cache:

• Storage: Redis/Memcached (configurable)
• Persistence: Automatic expiration
• Scalability: Works across multiple servers
• Performance: Fast read/write operations

API Response Codes

Security-related HTTP Status Codes

• 400 Bad Request - Invalid input or missing credentials
• 401 Unauthorized - Authentication failed
• 429 Too Many Requests - Rate limit exceeded
• 403 Forbidden - Account disabled or insufficient permissions

Response Examples

Rate Limited:

{
    'error': 'Too many login attempts. Please wait before trying again.',
    'retry_after': 8,
    'lockout_until': null
}

Account Locked:

{
    'error': 'Account temporarily locked due to too many failed login attempts',
    'retry_after': null,
    'lockout_until': 1705334622
}

Successful Login:

{
    'message': 'Login successful',
    'user': { /* user data */ },
    'session_created': true
}

Configuration Options

Rate Limiting Settings

You can adjust these constants in SecurityService.php:

private const RATE_LIMIT_ATTEMPTS = 5;      // Max attempts per window
private const RATE_LIMIT_WINDOW = 900;      // 15 minutes in seconds
private const LOCKOUT_DURATION = 3600;      // 1 hour in seconds
private const PROGRESSIVE_DELAY_BASE = 2;   // Base delay in seconds
private const MAX_PROGRESSIVE_DELAY = 60;   // Maximum delay in seconds

Security Headers

Customize security headers in the addSecurityHeaders() method:

// Content Security Policy
$response->addHeader('Content-Security-Policy', "default-src 'none'; frame-ancestors 'none';");

// Cache Control
$response->addHeader('Cache-Control', 'no-store, no-cache, must-revalidate, private');

Best Practices for Implementation

1. Always Use Security Service

// ✅ Correct - Use SecurityService
$response = $this->securityService->addSecurityHeaders($response);

// ❌ Incorrect - Direct response
return new JSONResponse($data);

2. Sanitize All Inputs

// ✅ Correct - Sanitize inputs
$sanitizedData = $this->securityService->sanitizeInput($data);

// ❌ Incorrect - Direct usage
$username = $_POST['username']; // Never do this

3. Validate Before Processing

// ✅ Correct - Validate first
$validation = $this->securityService->validateLoginCredentials($credentials);
if (!$validation['valid']) {
    return error_response($validation['error']);
}

// ❌ Incorrect - Process without validation
$user = $this->userManager->checkPassword($username, $password);

4. Log Security Events

All authentication attempts should be logged for monitoring and analysis.

5. Use Generic Error Messages

Avoid revealing system information:

// ✅ Correct - Generic message
return new JSONResponse(['error' => 'Invalid username or password']);

// ❌ Incorrect - Reveals information
return new JSONResponse(['error' => 'User john.doe does not exist']);

Monitoring and Alerting

Key Metrics to Monitor

1. Failed Login Rate - Sudden spikes may indicate attacks
2. Lockout Events - High frequency suggests ongoing attacks
3. IP Blocking - Geographic patterns may reveal bot networks
4. Response Times - Delays may indicate DoS attempts

Log Analysis

Search for security events in logs:

# Find failed login attempts
grep 'failed_login_attempt' /var/log/nextcloud.log

# Find rate limit exceeded events
grep 'rate_limit_exceeded' /var/log/nextcloud.log

# Find lockout events
grep 'locked_out' /var/log/nextcloud.log

Additional Security Recommendations

1. Use HTTPS Only

Ensure all API endpoints are served over HTTPS to prevent credential interception.

2. Regular Security Updates

Keep NextCloud and all dependencies updated to the latest versions.

3. Strong Password Policies

Implement password complexity requirements at the application level.

4. Two-Factor Authentication

Consider implementing 2FA for additional security layers.

5. Regular Security Audits

Perform regular penetration testing and security audits.

6. Web Application Firewall

Consider using a WAF for additional protection against common attacks.

Conclusion

The OpenConnector User API implements industry-standard security practices to protect against both XSS attacks and brute force attempts. The multi-layered approach ensures comprehensive protection while maintaining usability for legitimate users.

For any security concerns or questions, please refer to the code documentation or contact the development team.