Kibana is the so-called Front-end of your analyzing software. So it is important to be secured. I have also secured internal communication between Filebeat/Logstash to Elasticsearch, but this is a topic for another time. Let's start with securing Kibana's Front-end.

You SHOULD have either:

• Valid Certificate from Certification Authority (Let's encrypt is Free SSL CA)
• Self-Signed Certificate(Not Recommended)

Simple insert the following lines in the kibana.yml and all should be working normal:

server.ssl.enabled: true    <- Enable SSL/TLS
server.ssl.certificate: /root/SSLCert/cert.pem <- Provide the Certificate (Public key + CA Info)
server.ssl.key: /root/SSLCert/key.pem <- Provide the key file

Congrats, you have SSL/TLS connection :)