Create Kubernetes client configs with X509 certificates via openssl and the certificate-api

create-kubernetes-client-conf-users.sh

#!/bin/bash
set -e

# Make it priiittttty
RED='\033[0;31m'
NC='\033[0m'
GRN='\033[0;32m'

# Easy config
KEY_SIZE=4096
DST_DIR="certificates"
CLIENT_VALID_DAYS="365"
CERT_FILE_EXTENTION="pem"
AUTO_APPROVE_CSR="true"
CREATE_CLUSTER_ROLE_BINDING="true"
CLUSTER_ROLE=cluster-admin

####################### CHANGEME #######################
# NOTE: Activate the kube-context you want to create users in
# Add aditional names for mor clients (seperated by space)
# Usernames must be valid characters for mail addresses.
# You may also want to change the groups for the user configs in line 75+
CLIENTS=(test1 test2 test3)
CLUSTER_NAME=CHANGE_ME

# Cert data
COUNTRY="DE"
STATE="Hamburg"
CITY="Hamburg"
ORG="Company"
ORG_UNIT="Team_1"

#Set CWD
cd "$(dirname "$0")"
#Create DST-folder
mkdir -p "$DST_DIR"

#Check commands
if ! command -v openssl &>/dev/null; then
    echo -e "${RED}openssl not be found. Exit${NC}"
    exit 1
fi
if ! command -v jq &>/dev/null; then
    echo -e "${RED}jq not be found. Exit${NC}"
    exit 1
fi
if ! command -v kubectl &>/dev/null; then
    echo -e "${RED}kubectl not be found. Exit${NC}"
    exit 1
fi

# Get the current k8s context
k8s_current_context=$(kubectl config current-context)
# Get the cluster of the current context
k8s_current_cluster=$(kubectl config view -o jsonpath="{.contexts[?(@.name == \"$k8s_current_context\")].context.cluster}")
# Get the server of the current cluster
k8s_current_server=$(kubectl config view -o jsonpath="{.clusters[?(@.name == \"$k8s_current_cluster\")].cluster.server}")
# Get current cluster ca
k8s_current_server_ca=$(kubectl config view --raw -o jsonpath="{.clusters[?(@.name == \"$k8s_current_cluster\")].cluster.certificate-authority-data}")

# Ceck for openssl.conf
if [ -f openssl.conf ]; then
    echo "Using default values form local openssl.conf."
    OPENSSL_CONF_PARAM="-config openssl.conf"
fi

# Clients
for client in ${CLIENTS[@]}; do
    # Create cert if not exist
    if [ ! -f "$DST_DIR/$client.csr" ] || [ ! -f "$DST_DIR/$client.key" ]; then
        echo -e "${GRN}Creating ${client} key and sign request ${NC}"
        openssl req -new -newkey rsa:$KEY_SIZE -nodes -keyout $DST_DIR/$client.key -days $CLIENT_VALID_DAYS $OPENSSL_CONF_PARAM -batch -out $DST_DIR/$client.csr -subj "/CN=${client}/C=${COUNTRY}/ST=${STATE}/L=${CITY}/O=${ORG}/OU=${ORG_UNIT}/emailAddress=${client}@${ORG}.${COUNTRY,,}"
    fi

    kube_csr="apiVersion: certificates.k8s.io/v1
kind: CertificateSigningRequest
metadata:
  name: $client
spec:
  request: $(cat $DST_DIR/$client.csr | base64 | tr -d '\n')
  signerName: kubernetes.io/kube-apiserver-client
  groups:
    - system:unauthenticated
    - user:external-$client
    - user:external
  usages:
    - digital signature
    - key encipherment
    - client auth
"
    # Create csr
    echo "${kube_csr}" | kubectl apply -f -
done
echo -e "${GRN}You can inspect the created CertificateSigningRequest with \"kubectl get csr\"${NC}"
echo "---"

if [ "$AUTO_APPROVE_CSR" = "true" ]; then
    for client in ${CLIENTS[@]}; do
        if [ $(kubectl get csr $client -o json | jq .status.certificate) = "null" ]; then
            echo -e "${GRN}Approving ${client} csr ${NC}"
            kubectl certificate approve $client
        fi
    done
fi

# Check if approved anc create kubeconf
for client in ${CLIENTS[@]}; do
    if [ $(kubectl get csr $client -o json | jq .status.certificate) = "null" ]; then
        echo -e "${GRN}Please approve the csr's now an run the script again ${NC}"
        exit 1
    fi
    echo -e "${GRN}Creating kubeconf for ${client} ${NC}"
    kubectl get csr $client -o json | jq -r .status.certificate | base64 -d >$DST_DIR/$client.$CERT_FILE_EXTENTION
    kubectl --kubeconfig $DST_DIR/$client-kubeconf.yaml config set clusters.$CLUSTER_NAME.server $k8s_current_server
    kubectl --kubeconfig $DST_DIR/$client-kubeconf.yaml config set clusters.$CLUSTER_NAME.certificate-authority-data $k8s_current_server_ca
    kubectl --kubeconfig $DST_DIR/$client-kubeconf.yaml config set users.$CLUSTER_NAME-$client.client-key-data $(cat $DST_DIR/$client.key | base64 -w0)
    kubectl --kubeconfig $DST_DIR/$client-kubeconf.yaml config set users.$CLUSTER_NAME-$client.client-certificate-data $(cat $DST_DIR/$client.$CERT_FILE_EXTENTION | base64 -w0)
    kubectl --kubeconfig $DST_DIR/$client-kubeconf.yaml config set-context $CLUSTER_NAME --cluster $CLUSTER_NAME --user $CLUSTER_NAME-$client
    kubectl --kubeconfig $DST_DIR/$client-kubeconf.yaml config use-context $CLUSTER_NAME
done

# Create CRB
if [ "$CREATE_CLUSTER_ROLE_BINDING" = "true" ]; then
    for client in ${CLIENTS[@]}; do
        kube_crb="
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: external-user-$client
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: $CLUSTER_ROLE
subjects:
- apiGroup: rbac.authorization.k8s.io
  kind: User
  name: $client
"
        echo "${kube_crb}" | kubectl apply -f -
    done
else
    echo -e "${GRN}Please create RBAC rules for users${NC}"
fi

# Debug helper: https://www.sslshopper.com/article-most-common-openssl-commands.html
# cat $DST_DIR/$client.$CERT_FILE_EXTENTION $DST_DIR/$CA_FILE_NAME.$CERT_FILE_EXTENTION >$DST_DIR/$client-full.$CERT_FILE_EXTENTION

# To install the CA do:
# sudo cp certificates/ca.$CERT_FILE_EXTENTION /usr/local/share/ca-certificates/my-ca-cert.crt
# sudo update-ca-certificates
# Windows import
# https://community.spiceworks.com/how_to/1839-installing-self-signed-ca-certificate-in-windows

echo -e "${GRN}Everything generated succsesfully${NC}"

openssl.conf

[ req ]
default_bits       = 2048
distinguished_name = req_distinguished_name
req_extensions     = v3_req
promt              = no

# Default values can be overwirtten on CLI
[ req_distinguished_name ]
countryName                = DE
stateOrProvinceName        = Hamburg
localityName               = Hamburg
organizationName           = Company
commonName                 = client1
commonName_max             = 64
commonName_default         = client1
emailAddress                    = client1@example.com
emailAddress_max                = 64
emailAddress_default            = info@example.com

#Usage and SAN
[ v3_req ]
keyUsage = keyEncipherment, dataEncipherment, digitalSignature
extendedKeyUsage = serverAuth, clientAuth
subjectAltName = @alt_names

[alt_names]
DNS.1   =           localhost
DNS.2   =           *.localhost
DNS.3   =           *.k8s.localhost
DNS.4   =           host.docker.internal
DNS.5   =           gateway.docker.internal
DNS.6   =           kubernetes.docker.internal
DNS.7   =           *.local
DNS.8   =           *.internal
DNS.9   =           *.k8s.internal
IP.1    =           127.0.0.1
IP.2    =           ::1