Using the Strict-Security-Transport header

Enforcing Https is the default these days, however some websites still open the 80 port for various reasons. 
When a browser sends a request over HTTP, the web server may redirect the browser to the https version.

The Strict-Security-Transport header is used to prevent the browser from calling the HTTP site every time before being redirected. The header instructs the browser to remember for a specified period of time that this resource should be accessed only with HTTPS.

The official term for this setting is HSTS - Http Strict Transport Security