May 12, 2026 Layer 4 — API Key Authentication: Securing Machine-to-Machine Requests May 12, 2026 Layer 2 — Tenant Resolution: How a Single API Instance Serves Multiple Customers Safely May 12, 2026 Layer 1 — nginx as Your Security Perimeter: SSL Termination and Access Logging May 12, 2026 Security Auditing in a Multi-Tenant SaaS: Layered Filters, JWT, and API Keys May 12, 2026 Layer 3 — JWT Authentication: Stateless Identity with Short-Lived Tokens