What Is HSTS and How Does It Strengthen HTTPS Security?

**Executive Summary:** This report provides an overview of HTTP Strict Transport Security (HSTS), explaining how HSTS enforces HTTPS to prevent downgrade and man-in-the-middle attacks, outlines best practices (long max-age, includeSubDomains, preload list, and strong TLS), and highlights third-party/supply-chain risks and monitoring approaches for detecting missing or misconfigured HSTS headers.