Ensure Basic Authentication is disabled on Kubernetes Engine Clusters

Description: 

Basic authentication allows a user to authenticate to the cluster with a username and password and it is stored in plain text without any encryption. Disabling Basic authentication will prevent attacks like brute force. Its recommended to use either client certificate or IAM for authentication.

Solution: 

Plaintext username/password must be disabled. Use client-certificate policy as stipulated above.

Reference: 

https://cloud.google.com/kubernetes-engine/docs/concepts/security-overview