create-user.sh

#!/bin/bash

# This script uses Kubernetes CertificateSigningRequest (CSR) to a generate a
# certificate signed by the Kubernetes CA itself.
# It requires cluster admin permission.
#
# e.g.: ./create-user.sh alice oil
#       where `oil` is the Tenant and `alice` the owner

# Check if OpenSSL is installed
if [[ ! -x "$(command -v openssl)" ]]; then
    echo "Error: openssl not found"
    exit 1
fi

# Check if kubectl is installed
if [[ ! -x "$(command -v kubectl)" ]]; then
    echo "Error: kubectl not found"
    exit 1
fi

USER=$1
TENANT=$2

if [[ -z ${USER} ]]; then
    echo "User has not been specified!"
    exit 1
fi

if [[ -z ${TENANT} ]]; then
    echo "Tenant has not been specified!"
    exit 1
fi

GROUP=capsule.clastix.io

TMPDIR=$(mktemp -d)
echo "creating certs in TMPDIR ${TMPDIR} "

openssl genrsa -out ${TMPDIR}/tls.key 2048
openssl req -new -key ${TMPDIR}/tls.key -subj "/CN=${USER}/O=${GROUP}" -out ${TMPDIR}/${USER}-${TENANT}.csr

# Clean any previously created CSR for the same user.
kubectl delete csr ${USER}-${TENANT} 2>/dev/null || true

# Create a new CSR file.
cat <<EOF > ${TMPDIR}/${USER}-${TENANT}-csr.yaml
apiVersion: certificates.k8s.io/v1beta1
kind: CertificateSigningRequest
metadata:
  name: ${USER}-${TENANT}
spec:
  groups:
  - system:authenticated
  request: $(cat ${TMPDIR}/${USER}-${TENANT}.csr | base64 | tr -d '\n')
  usages:
  - digital signature
  - key encipherment
  - client auth
EOF

# Create the CSR
kubectl apply -f ${TMPDIR}/${USER}-${TENANT}-csr.yaml

# Approve and fetch the signed certificate
kubectl certificate approve ${USER}-${TENANT}
kubectl get csr ${USER}-${TENANT} -o jsonpath='{.status.certificate}' | base64 --decode > ${TMPDIR}/tls.crt

# Create the kubeconfig file
CONTEXT=$(kubectl config current-context)
CLUSTER=$(kubectl config view -o jsonpath="{.contexts[?(@.name == \"$CONTEXT\"})].context.cluster}")
SERVER=$(kubectl config view -o jsonpath="{.clusters[?(@.name == \"${CLUSTER}\"})].cluster.server}")
CA=$(kubectl config view --flatten -o jsonpath="{.clusters[?(@.name == \"${CLUSTER}\"})].cluster.certificate-authority-data}")

cat > ${USER}-${TENANT}.kubeconfig <<EOF
apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: $CA
    server: ${SERVER}
  name: ${CLUSTER}
contexts:
- context:
    cluster: ${CLUSTER}
    user: ${USER}
  name: ${USER}-${TENANT}
current-context: ${USER}-${TENANT}
kind: Config
preferences: {}
users:
- name: ${USER}
  user:
    client-certificate-data: $(cat ${TMPDIR}/tls.crt | base64 | tr -d '\n')
    client-key-data: $(cat ${TMPDIR}/tls.key | base64 | tr -d '\n')
EOF

echo "kubeconfig file is:" ${USER}-${TENANT}.kubeconfig
echo "to use it as" ${USER} "export KUBECONFIG="${USER}-${TENANT}.kubeconfig