It is a best practice not to use security key (whenever possible). But currently for Forseti on GKE, IAM service account key is obtained from GCP and added as a secret to kubernetes.
Per discussion with @kevensen, it is possible to create a dedicated Forseti nodepool in the cluster and bind the SA to the nodes, without using a key. i.e. "taint" these nodes as described above for the sole-use of Forseti.
It is a best practice not to use security key (whenever possible). But currently for Forseti on GKE, IAM service account key is obtained from GCP and added as a secret to kubernetes.
Per discussion with @kevensen, it is possible to create a dedicated Forseti nodepool in the cluster and bind the SA to the nodes, without using a key. i.e. "taint" these nodes as described above for the sole-use of Forseti.