WP-Cassify behind loadbalancer which can’t directly address CAS server

We have our CAS server, and our wordpress server behind a load balancer.

With the way it’s configured, the wordpress server can’t access the CAS server by the same url as a user would. (It doesn’t allow for the connection to come back in)

To get round this, I’m editing wp_cassify_plugin.php (around line 343)
$service_validate_url = $wp_cassify_base_url .
$wp_cassify_service_validate_servlet . ‘?’ .
$this->wp_cassify_default_service_ticket_parameter_name . ‘=’ . $service_ticket . ‘&’ .
$this->wp_cassify_default_service_service_parameter_name .’=’ . $service_url;

to change $wp_cassify_base_url to being something which it can address directly.

Obviously, directly editing the plugin files is to be avoided. Is there any chance we can get an optional additional parameter for this?