I had some sites on shared hosting environment for which I had to do http to https redirection with .htaccess file. I did 302 redirection intentionally so that in case of error, browser doesn’t cache redirection. You can aslo make permanent 301 redirect if needed.
This is nice and simple way to do it:
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=302]