How to connect to Data Node to fix long messages not logged #61

Hi, I want to try to apply one of these solutions, for example, Graylog2/graylog2-server#873 (comment).
Using the "open-core" compose and default configurations on setup.
How do I connect to the Data Node to apply the fix? If I for example curl -k -X GET "https://localhost:9200/_cluster/health?pretty=true" I get "Authentication finally failed". Do I need to extract the certificate to connect or something similar? help appreciated.