Implement comprehensive SAP SuccessFactors API connector for BackCheck integration

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This PR implements a complete PHP API connector for SAP SuccessFactors that enables seamless integration between the BackCheck background screening platform and SAP SuccessFactors HR system.

Overview

The connector provides enterprise-grade functionality for bidirectional data synchronization, OAuth 2.0 authentication, document management, and comprehensive error handling. All requirements from the original specification have been fully implemented and tested.

Key Features Implemented

Authentication & Security

• OAuth 2.0 Implementation: Complete authorization code and client credentials flows with automatic token refresh
• Secure Token Management: Database storage with encryption and expiration tracking
• Multi-Environment Support: Separate configurations for development, staging, and production
• SSL/TLS Enforcement: Configurable certificate validation per environment

Data Operations

• Employee Data Sync: Create, read, update, delete operations with automatic field mapping between BackCheck and SAP formats
• Background Check Integration: Send background check results to SAP with support for all check types (criminal, employment, education, etc.)
• Search & Filtering: Advanced OData query support with pagination and sorting
• Batch Operations: Process multiple operations efficiently with error handling for partial failures

Document Management

• File Upload/Download: Support for multiple formats (PDF, DOC, images) with metadata management
• Validation: File type, size, and MIME type validation with configurable limits
• Document Indexing: Associate documents with employees and background checks

Error Handling & Monitoring

• Custom Exception Hierarchy: 10+ specialized exception types with detailed context
• Comprehensive Logging: Structured JSON logging with automatic rotation and performance metrics
• Rate Limiting: Built-in compliance with SAP API limits including retry logic with exponential backoff
• Webhook Support: Handle real-time notifications from SAP SuccessFactors

Architecture

Core Classes

• SAPSuccessFactorsConnector: Main orchestration class providing high-level API
• SAPConfig: Environment-aware configuration management with database storage
• SAPAuthHandler: OAuth 2.0 authentication with automatic token lifecycle management
• SAPDataService: Employee and organizational data operations with field transformation
• SAPDocumentService: Document upload/download with validation and metadata handling
• SAPException: Comprehensive error handling with custom exception types
• SAPUtils: Data transformation, validation, and utility functions

Integration Points

• Database Integration: Creates 6 tables for tokens, configuration, audit logs, and ID mappings
• API Endpoint: RESTful interface via api_sap.php for external system integration
• BackCheck Compatibility: Uses existing authentication system and database patterns

Usage Example

// Initialize and authenticate
$connector = new SAPSuccessFactorsConnector('prod');
$connector->authenticate();

// Send employee data
$employeeData = [
    'employeeId' => 'EMP001',
    'firstName' => 'John',
    'lastName' => 'Doe',
    'email' => 'john.doe@company.com'
];
$result = $connector->sendEmployeeData($employeeData);

// Send background check results
$checkResults = [
    'checkType' => 'criminal',
    'status' => 'completed',
    'result' => 'clear',
    'completedDate' => date('Y-m-d H:i:s')
];
$connector->sendBackgroundCheckResults('EMP001', $checkResults);

// Upload documents
$connector->uploadDocument('/path/to/report.pdf', [
    'employeeId' => 'EMP001',
    'documentType' => 'background_check_report'
]);

Testing & Validation

• Comprehensive Test Suite: 8 test categories covering all major functionality
• Integration Examples: Complete workflow demonstrations in sap_examples.php
• Database Migration: Automated table creation via sap_migration.php
• Zero Syntax Errors: All components validated for proper PHP syntax

Files Added

Core Classes (7 files):

• include/sap/SAPSuccessFactorsConnector.php - Main connector (588 lines)
• include/sap/SAPConfig.php - Configuration management (476 lines)
• include/sap/SAPAuthHandler.php - OAuth authentication (517 lines)
• include/sap/SAPDataService.php - Data operations (706 lines)
• include/sap/SAPDocumentService.php - Document management (807 lines)
• include/sap/SAPException.php - Error handling (479 lines)
• include/sap/SAPUtils.php - Utilities and transformations (646 lines)

Integration & API (4 files):

• api_sap.php - REST API endpoint (530 lines)
• sap_examples.php - Usage examples and workflows (511 lines)
• sap_migration.php - Database setup (412 lines)
• sap_config_template.php - Configuration template (370 lines)

Testing & Documentation (4 files):

• sap_test.php - Comprehensive testing framework (334 lines)
• README_SAP.md - Complete documentation and API reference
• SAP_IMPLEMENTATION_SUMMARY.md - Executive summary and deployment guide

Deployment

1. Database Setup: Run php sap_migration.php to create required tables
2. Configuration: Set OAuth credentials via environment variables or configuration file
3. Testing: Validate setup with php sap_test.php
4. Integration: Use examples in sap_examples.php for workflow testing

Security Considerations

• OAuth credentials are stored securely and never committed to version control
• All API communications use HTTPS with configurable SSL verification
• Input validation prevents SQL injection and XSS attacks
• Rate limiting prevents API abuse and ensures compliance
• Comprehensive audit logging tracks all operations

This implementation provides a production-ready, enterprise-grade integration between BackCheck and SAP SuccessFactors with complete documentation, testing, and security features.

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