WWW Redirection in an HTACCESS File - .htaccess

Question

I have an htaccess file for a React app at https://searchglutenfree.com/. I want it to automatically rewrite https://www.searchglutenfree.com/ to https://searchglutenfree.com/ while keeping all the params during the redirection.
I found this great default htaccess template on GitHub (https://gist.github.com/iheartmedia-matt/253ccb6183fdeaa5619f615f2cb5a58b), and getting the www to redirect is the last thing I need. Anyone know what I need to add and where in the file to get the WWW rewrite?
<ifModule mod_rewrite.c>
#######################################################################
# GENERAL #
#######################################################################
# Make apache follow sym links to files
Options +FollowSymLinks
# If somebody opens a folder, hide all files from the resulting folder list
IndexIgnore */*
#######################################################################
# REWRITING #
#######################################################################
# Enable rewriting
RewriteEngine On
# If its not HTTPS
RewriteCond %{HTTPS} off
# Comment out the RewriteCond above, and uncomment the RewriteCond below if you're using a load balancer (e.g. CloudFlare) for SSL
# RewriteCond %{HTTP:X-Forwarded-Proto} !https
# Redirect to the same URL with https://, ignoring all further rules if this one is in effect
RewriteRule ^(.*) https://%{HTTP_HOST}/$1 [R,L]
# If we get to here, it means we are on https://
# If the file with the specified name in the browser doesn't exist
RewriteCond %{REQUEST_FILENAME} !-f
# and the directory with the specified name in the browser doesn't exist
RewriteCond %{REQUEST_FILENAME} !-d
# and we are not opening the root already (otherwise we get a redirect loop)
RewriteCond %{REQUEST_FILENAME} !\/$
# Rewrite all requests to the root
RewriteRule ^(.*) /
</ifModule>
<IfModule mod_headers.c>
# Do not cache sw.js, required for offline-first updates.
<FilesMatch "sw\.js$">
Header set Cache-Control "private, no-cache, no-store, proxy-revalidate, no-transform"
Header set Pragma "no-cache"
</FilesMatch>
</IfModule>

Answer 1

If you don’t need this to be dynamic regarding the host name, then I would add a Condition that checks if the host name started with www. after the one that checks for %{HTTPS} off, and add the [OR] flag to the former - and then simply hard-code the host name in the substitution URL of the following Rule.
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP_HOST} ^www\.
RewriteRule ^(.*) https://searchglutenfree.com/$1 [R,L]
If you replace everything between the comments # If its not HTTPS and # If we get to here, it means we are on https:// in your .htaccess you had shown above with that, it should work.

Answer 2

In order to set up the desired redirect, www.example.com to example.com or vice versa, you must have an A record for each name.
To redirect users from www to a plain, non-www domain, insert this configuration:
in your .htaccess:
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]