Using the TransportClient with ECK

We have a legacy application which uses the Java TransportClient to access the ES API on port 9300, which we would like to operate with the ES operator. It seems that the ES instance created by ECK only exposes the REST API on port 9200.

Is it possible to use the API on port 9300? I tried to expose it via a Service, but it is secured by client certificate authentication and I cannot figure out how to create a valid certificate.

First of all, Transport Client is currently deprecated and we don't suggest to rely on it in the future.
If disabling client authentication is an option for you, then you can do it as described in

Thanks for your prompt answer. I followed the instructions and disabled client certificate authentication, the application can now successfully connect to ES.

We are aware that the Transport Client is deprecated, but until the migration is implemented we need an intermediate solution.