To have a common root CA, you usually use a PKI. That’s what we do at work for internal SSL sites; not trivial, though.
With this, you “just” install the root CA in both servers, so they can check their mutual certs.
in config.php look up config.php.sample
How do you need to have a PKI root CA? What tools or commands are needed? Can you tell me the specific operation steps?
Thanks!