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#!/usr/bin/bash
#############################################################
# Title: Script to provision the client CSR and generat the #
#        the client SSL certificate.                        #
#############################################################

# Create CSR resource template.
function create_csr_resource() {
    K8SUSER=$1
    DCNM=$2
    FILE=${K8SUSER}_${DCNM}_csr_res.yaml
    echo "
apiVersion: certificates.k8s.io/v1
kind: CertificateSigningRequest
metadata:
  name: ${K8SUSER}_${DCNM}csr
spec:
  groups:
  - system:authenticated
  request: ${BASE64_CSR}
  signerName: kubernetes.io/kube-apiserver-client
  usages:
  - digital signature
  - key encipherment
  - client auth" > $FILE
}

# Create CLUSTER ROLE resource template
function create_cluster_role() {
    K8SUSER=$1
    DCNM=$2
    FILE=${K8SUSER}_${DCNM}_cluster_role_res.yaml
    echo "
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: clustrole_${K8SUSER}_${DCNM}
rules:
- apiGroups: [\"\"]
  resources: ["nodes", "namespaces", "pods", "services"]
  verbs: ["get", "list", "watch"]" > $FILE
}

# Create CLUSTER ROLE BINDING template
function create_cluster_role_binding() {
    K8SUSER=$1
    DCNM=$2
    FILE=${K8SUSER}_${DCNM}_cluster_rolebinding_res.yaml
    echo "
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: clustrolebind_${K8SUSER}_${DCNM}
roleRef:
  kind: ClusterRole
  name: clustrole_${K8SUSER}_${DCNM}
  apiGroup: rbac.authorization.k8s.io
subjects:
- kind: User
  name: ${K8SUSER}
  apiGroup: rbac.authorization.k8s.io" > $FILE
}

function valid_ip() {
    local  ip=$1
    local  stat=1

    if [[ $ip =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
        OIFS=$IFS
        IFS='.'
        ip=($ip)
        IFS=$OIFS
        [[ ${ip[0]} -le 255 && ${ip[1]} -le 255 \
            && ${ip[2]} -le 255 && ${ip[3]} -le 255 ]]
        stat=$?
    fi
    return $stat
}

# Start of the script 
if [ "$#" -ne 2 ]; then
    echo "Please provide the username and IP of the DCNM"
    echo
    exit 1
else

    # Check if user have required K8s privileges
    LINUX_USER=$(whoami)
    K8S_CONF_PATH=""
    echo 
    echo "Hello ${LINUX_USER}! I am going to help you generate K8s cluster CA and K8s client certificate." 

    if [ ${LINUX_USER} == "root" ] ; then
        # You are root
        if [ ! -d "/root/.kube" ] ; then
            echo 
            echo "Directory /root/.kube does not exists."
            echo "User ${LINUX_USER} does not have required K8s privileges"
            echo "Please make sure you are logged into K8s cluster's master node"
            echo 
            exit 1
        else
            K8S_CONF_PATH=/${LINUX_USER}/.kube/config
        fi
    else
        # You are not root
        if [ ! -d "/home/${LINUX_USER}/.kube" ] ; then
            echo 
            echo "Directory /home/${LINUX_USER}/.kube does not exists."
            echo "User ${LINUX_USER} does not have required K8s privileges"
            echo "Please make sure you are logged into K8s cluster's master node"
            echo 
            exit 1
        else
            K8S_CONF_PATH=/home/${LINUX_USER}/.kube/config
        fi
    fi

    # Check if K8s config file exist
    if [ ! -f ${K8S_CONF_PATH} ]; then
        echo 
        echo "${K8S_CONF_PATH} file does not exist"
        echo "K8s CA certificate can not be exported"
        echo "Please make sure you are logged into K8s cluster's master node"
        echo
        exit 1
    fi

    K8SUSER=$1
    DCNM=$2
    K8S_CA_CRT="k8s_cluster_ca.crt"

    # Validate the IP address
    if valid_ip $DCNM; then
        echo -e
    else
        echo "${2} is not a valid IP address"
        echo
        exit 1
    fi

    # Validate the CSR file format
    if [ ${K8SUSER: -4} == ".csr" ]; then
        K8SUSER=${K8SUSER%.csr}
    fi

    if [ ! -f "./${K8SUSER}.csr" ]; then
        echo
        echo "./${K8SUSER}.csr does not exist"
        echo "CSR file is required for creation of client certificate"
        echo
        exit 1
    fi

    echo "Generating certificate for ${K8SUSER} for DCNM ${DCNM}"
    echo

    # Encoding the .csr file in base64
    export BASE64_CSR=$(cat ./${K8SUSER}.csr | tr -d '\n')

    # Create the CSR resource in K8s cluster
    create_csr_resource $K8SUSER $DCNM

    # Delete if the CSR resource already exist. We need a fresh one.
    kubectl delete csr ${K8SUSER}_${DCNM}csr &> /dev/null
    status=$?
    if test $status -eq 0
    then
        echo "./${K8SUSER}_${DCNM}csr CSR resource already exist, removing it"
    else
        echo "./${K8SUSER}_${DCNM}csr CSR resource does not exist, creating it"
    fi

    # Create the CertificateSigninRequest resource
    kubectl apply -f ${K8SUSER}_${DCNM}_csr_res.yaml

    # Check the status of the newly created CSR
    kubectl get csr

    # Approve this CSR
    echo "Approving the CSR"
    kubectl certificate approve ${K8SUSER}_${DCNM}csr

    # Check the status of the newly created CSR
    kubectl get csr

    # Create role resource definition
    kubectl delete clusterrole clustrole_${K8SUSER}_${DCNM} &> /dev/null
    create_cluster_role $K8SUSER $DCNM
    kubectl apply -f ${K8SUSER}_${DCNM}_cluster_role_res.yaml

    # Create role binding definition
    kubectl delete clusterrolebinding clustrolebind_${K8SUSER}_${DCNM} &> /dev/null
    create_cluster_role_binding $K8SUSER $DCNM
    kubectl apply -f ${K8SUSER}_${DCNM}_cluster_rolebinding_res.yaml

    # Extract the client certificate
    echo "Extracting the user SSL certificate"
    kubectl get csr ${K8SUSER}_${DCNM}csr -o jsonpath='{.status.certificate}' > ${K8SUSER}_${DCNM}.crt
    echo "" >> ${K8SUSER}_${DCNM}.crt

    # Export the K8s cluster CA cert
    if [ -f ${K8S_CONF_PATH} ]; then
        echo "Exporting K8s CA certificate"
        cat ${K8S_CONF_PATH} | grep certificate-authority-data | awk -F ' ' '{print $2}' > ${K8S_CA_CRT}
    fi
    echo
    echo "--------------------------------------------------------------"
    echo "Notes: " 
    echo "1. The K8s CA certificate is copied into ${K8S_CA_CRT} file."
    echo "      This to be copied into \"Cluster CA\" field."
    echo "2. The client certificate is copied into ${K8SUSER}_${DCNM}.crt file."
    echo "      This to be copied into \"Client Certificate\" field."
    echo "--------------------------------------------------------------"
    echo
fi