information of the authenticated user

When you see Define clusters, users, and contexts, you realize you need to get the information associated with a defined context.

kubectl config --kubeconfig=config-demo use-context dev-frontend
kubectl config --kubeconfig=config-demo view --minify

The output shows configuration information associated with the dev-frontend context:

apiVersion: v1
clusters:
- cluster:
    certificate-authority: fake-ca-file
    server: https://1.2.3.4
  name: development
contexts:
- context:
    cluster: development
    namespace: frontend
    user: developer
  name: dev-frontend
current-context: dev-frontend
kind: Config
preferences: {}
users:
- name: developer
  user:
    client-certificate: fake-cert-file
    client-key: fake-key-file

assigned role and assigned cluster role.

You can list roles for all users or clusters, but you still need to parse the result to get the one for a user or a cluster.
Example: "kubectl and seeing (cluster)roles assigned to subjects".