How to force www. in a generic way with .htaccess

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
</IfModule>

source: https://www.dataplugs.com/tc/kb/使用-htaccess-檔案強制將-http-導向-https-ssl/