How to redirect all variations of a domain to https version?
example.com is the naked version of www.example.com. In the settings for the domain, add an A name pointing to IP of your server. 



Add a C Name that points to the www version at the same IP.



If you are running Apache, in the virtual host settings add both Servername and ServerAlias.

&lt;VirtualHost *:80&gt;                                                                                                          
        ServerName example.com
        ServerAlias www.example.com 


This will make sure that your server listens both the naked domain and normal domains and points them to you code folder for execution. 

Make sure the .htaccess file contains the following lines.

  RewriteEngine on

  # Set "protossl" to "s" if we were accessed via https://.  This is used later
  # if you enable "www." stripping or enforcement, in order to ensure that
  # you don't bounce between http and https.
  RewriteRule ^ - [E=protossl]
  RewriteCond %{HTTPS} on
  RewriteRule ^ - [E=protossl:s]


This code just sets a flag called protossl, if you have visited using https. This will ensure that you don't have infinite redirections between http and https as mentioned in the comments.

Comment out all other settings related to http and https redirection, and add the following lines. 

#
# Rewrite http(s)://example.com to https://www.example.com
#
RewriteCond "%{HTTP_HOST}" "!^www\." [NC]
RewriteCond "%{HTTP_HOST}" "!^$"
RewriteRule ^ https://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

#
# Rewrite http://www.example.com to https://www.example.com
#
RewriteCond %{HTTPS} off
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]


This code was provided by https://www.drupal.org/u/mdrescher on 
https://www.drupal.org/forum/support/post-installation/2018-04-15/forcing-to-https#comment-12723535.

These changes will make sure that all six variations example.com, www.example.com, http://example.com, http://www.example.com, https://example.com, https://www.example.com are redirection https://www.example.com