HSTS (HTTP Strict Transport Security) is a mechanism that helps protect your website from man-in-the-middle attacks including protocol downgrade attacks and cookie hijacking. This is accomplished through a response header that browsers receive when accessing your website.
Preventing Insecure Communications
In addition to supporting HTTPS, we also include HSTS support. With this technology, browsers will prevent insecure communications between the browser and the server and will require all data be sent over HTTPS.
Once a supported browser receives this header, that browser will prevent any communications from being sent over HTTP to the specified domain and will instead send all communications over HTTPS.