What is HSTS?

HTTP Strict Transport Security (HSTS) is a web security policy mechanism that helps to protect websites against protocol downgrade attacks and cookie hijacking. It allows a web server to declare that web browsers should only interact with it using secure HTTPS connections, and never via the insecure HTTP protocol. HSTS is commonly used to enforce HTTPS usage and prevent man-in-the-middle attacks that could attempt to redirect users to a malicious HTTP site.