Seen plenty slight variations to use in htaccess. These work ok for me.
Code:
# ensure www
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteRule ^ https://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
# ensure https
RewriteCond %{HTTP:X-Forwarded-Proto} !https
RewriteCond %{HTTPS} off
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]