Reverse proxy onto a WordPress page?

Solution:

Server setup

Before you even touch WordPress, you need to make sure that the server hosting B is ready to accept requests and forward requests for any URL to A.

Assuming you have Apache setup and working, let’s make sure mod_proxy is enabled. With root or sudo privileges, run:

a2enmod proxy_http
service apache2 restart

Then, open the Apache virtual hosts config file, and add:

ProxyPreserveHost On
ProxyRequests Off   
<Location /blog>
    ProxyPass http://blog.mysite.com 
    ProxyPassReverse http://blog.mysite.com  
    Order allow,deny   
     Allow from all
</Location>

Now you got to make sure that all URLs (category pages, single post pages) also display correctly on site B.

For this, log into WordPress admin using the original login link: blog.mysite.com/wp-login.php.

Go to Settings > General, and update the “Site address (URL)” field to B (supersite.com/blog).

Credits : https://tanyanam.com/2015/07/13/setting-up-wordpress-behind-reverse-proxy/