Unauthorized issues when adding new kubernetes master
To add a new master to kubernetes cluster, you need to copy four files from your existing kubernetes master certificate directory before doing kubeadm init on new master. Those files are ca.crt, ca.key, sa.pub, sa.key and copy these files to /etc/kubernetes/pki folder on new master. If you don't copy the sa* files your kubernetes master will be into NotReady state and will have those errors.
For more information on how to setup kubernetes multi master, please check out my blog on kubernetes high availability:
https://velotio.com/blog/2018/6/15/kubernetes-high-availability-kubeadm