The *GET /kubeadm/kubeconfig/<instance-id>* operation returns a
configuration document for `kubeadm` to add the node to the cluster as a
worker. The document is derived from the kubeconfig stored in the
`cluster-info` ConfigMap, which includes the external URL of the
Kubernetes API server and the root CA certificate used in the cluster.
The bootstrap token assigned to the specified instance is added to the
document for `kubeadm` to use for authentication. The kubeconfig is
stored in the ConfigMap as a string, so extracting data from it requires
deserializing the YAML document first.
In order to access the cluster information ConfigMap, the service
account bound to the pod running the provisioner service must have the
appropriate permissions.
Dustin