50. Capstone: Secure API Service Architecture

A production-grade PHP API service combines many topics from this course: PSR-4 autoloaded classes organized by namespace, dependency injection for testability, PDO with prepared statements for all database access, and password_hash()/password_verify() for credential storage. Input validation, CSRF protection on stateful endpoints, and htmlspecialchars()/JSON encoding for output all defend against injection and XSS.

Around this core, OPcache (and JIT where CPU-bound) improves performance, PHPUnit tests with data providers and mocks guard against regressions, custom exception hierarchies produce clean HTTP error responses, and outbound integrations (whether a payment gateway's REST API or a blockchain node's JSON-RPC endpoint) are wrapped behind cURL calls with careful error checking and, where needed, arbitrary-precision math for large numeric values. Together these practices form the backbone of a secure, maintainable, and performant PHP application.