Resolved: What can cause: There was a problem authenticating with your cluster. In Gitlab?

Question:

Hi I’m trying to authenticate a Kubernetes Cluster with Gitlab. Im doing it via the Certificate method and followed the guide on gitlabs documentation
But it doesn’t connect. Gitlab tells me:
There was a problem authenticating with your cluster. Please ensure your CA Certificate and Token are valid. 
There was a firewall issue my boss thought would be the reason. But now that the Firewall issue has been resolved and the problem persists I don’t know what could be the cause. Is there some log file that could help me pin down the reason?
One thing I noticed is that kubectl cluster-info shows the url to be a private IP: https://10.254.1.3:6443. I don’t know for sure, but I thought I’ve dealt with a few programs that only respond to requests within the network when the url is local. Could this be an issue?
I tried changing the server IP in .kube/config to the public IP but then kubectl cluster-info did not terminate anymore.

Answer:

The problem was that the Cluster was not accessible from outside. I found a solution on this question. I had to generate new certificates that also certify the public IP.
First I had to remove the certificates:
sudo rm /etc/kubernetes/pki/apiserver.*
and then generate new ones with the public IP:
sudo kubeadm init phase certs apiserver --apiserver-cert-extra-sans=<public_ip>

If you have better answer, please add a comment about this, thank you!

Source: Stackoverflow.com