Terraform and the CLI offer easy access to a working config file. On the CLI, one can run:

openstack coe cluster config <cluster-name> --dir /tmp/

And get a ready to use admin config in /tmp/ to connect to kubernetes (Either by placing it in their default path, probably .kube/config or using the env var export KUBECONFIG=/home/...)

Horizon rather tries to get one to create an RSA key, and get it signed by the ca, then to do some kubectl enchantments to generate the config, followed by creating roles (Perhaps there is a way to have the key act as admin? Not sure). This shouldn't be the case.

The "Sign Certificate" button in horizon should be replaced with something that runs the command above and offers a functioning config to the user.