Forzar el https usando .htaccess
Forcing the domain to serve securely using HTTPS (for any site)
The following forces any http request to be rewritten using https. For example, the following code forces a request to http://example.com to load https://example.com. It also forces directly linked resources (images, css, etc.) to use https:
RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301,NE]
Header always set Content-Security-Policy "upgrade-insecure-requests;"
If this isn’t working for you, first check your line endings. Copy/paste from your web browser into a text editor may not work right, so after pasting into your text editor you should delete each line break and add it back in (line break = return key).