RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

RewriteEngine On
RewriteCond %{HTTP_HOST} ^www.xxx [NC]
RewriteRule ^(.*)$ https://xxx/$1 [L,R=301]

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ https://xxx/ [L,R=301]