Domain redirection is not working perfect - .htaccess

Question

I have a website setup in codeigniter. In config.php, baseurl is
https://example.com
In htaccess, following code has been written:
RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*) https://example.com/$1 [R,L]
php_value date.timezone Asia/Kolkata
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond $1 !^(index.php|resources|robots.txt)
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?/$1 [L,QSA]
</IfModule>
<IfModule mod_headers.c>
SetEnvIf Origin "https://(www|sub1|sub2|sub3).example.com)$" ACAO=$0
Header set Access-Control-Allow-Origin "%{ACAO}e" env=ACAO
Header set Access-Control-Allow-Methods "GET"
</IfModule>
There are four variations of domains:
https://www.example.com
http://www.example.com
http://example.com
https://example.com
I want 1, 2 and 3 redirect to 4. Witht he above htaccess code, 2 and 3 are redirecting to 4.
But,
1 is not redirecting to 4
please suggest a solution.

Answer 1

To remove www and enforce https, replace your first redirect rule with this one:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^www\. [NC,OR]
RewriteCond %{HTTPS} !on
RewriteCond %{HTTP_HOST} ^(?:www\.)?(.+)$ [NC]
RewriteRule ^ https://%1%{REQUEST_URI} [R=301,L,NE]
RewriteCond $1 !^(index.php|resources|robots.txt)
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?/$1 [L,QSA]
<IfModule mod_headers.c>
SetEnvIf Origin "https://(www|sub1|sub2|sub3).example.com)$" ACAO=$0
Header set Access-Control-Allow-Origin "%{ACAO}e" env=ACAO
Header set Access-Control-Allow-Methods "GET"
</IfModule>