How to keep HTTP_HOST of backend server when forwarding web traffic - apache

Question

For forwarding an internal website (i.e. normally not available on internet) to internet I use ProxyPass in Apache.
I have the following setup:
Backend server: An internal laptop or Raspberry PI or virtual machine running an Apache web server on macOS or Linux, accessible in my home wifi. From that machine the following reverse SSH tunnel is run.
Frontend server: A VPS rented running Ubuntu running Apache web server.
When I perform a reverse SSH tunnel to the VPS :
ssh -N -p 22 -R 1081:127.0.0.1:80 root#myVPS
I can access my internal localhost site on https://forward.example.com, just like it behaves internally.
But the glitch is that the $_SERVER["HTTP_HOST"] now returns "localhost:1081" as specified in the ssl.conf.
In PHP I get the remote IP address by $_SERVER['HTTP_X_FORWARDED_FOR'] rather than $_SERVER['REMOTE_ADDR'], so that works fine.
There is also a $_SERVER['HTTP_X_FORWARDED_HOST'] which shows 'forward.example.com'.
Some posts on the internet advised me to specify ProxyPreserveHost on, but enabling that makes things worse: I get a redirect loop.
Is there a way to let Apache force $_SERVER['HTTP_X_FORWARDED_HOST'] ('forward.example.com' in my example) into $_SERVER"HTTP_HOST"]?
Virtual host section in ssl.conf:
<VirtualHost *:443>
SSLEngine on
DocumentRoot /var/www/html/test/
ServerName forward.example.com
LogLevel Debug
ErrorLog ${APACHE_LOG_DIR}/forward-error.log
CustomLog ${APACHE_LOG_DIR}/forward.log combined
SSLCertificateFile /root/.acme.sh/forward.example.com/fullchain.cer
SSLCertificateKeyFile /root/.acme.sh/forward.example.com/forward.example.com.key
# SSLCertificateChainFile /root/.acme.sh/forward.example.com/fullchain.cer
SSLProxyEngine On
ProxyRequests Off
# This causes a redirect loop !!!
# ProxyPreserveHost on
# https://httpd.apache.org/docs/2.4/mod/mod_proxy_wstunnel.html
ProxyPass / http://localhost:1081/
ProxyPassReverse / http://localhost:1081/
RewriteCond %{HTTP:Upgrade} websocket [NC]
RewriteCond %{HTTP:Connection} upgrade [NC]
RewriteRule ^/?(.*) "ws://localhost:1081/$1" [P,L]
</VirtualHost>