#!/usr/bin/env bash
# Installs OpenVPN server on CentOS 7

# Check yo' privilege
[[ $(id -u) != 0 ]] && echo 'You must run this script as root!' && exit 1

################################################################################
################################## VARIABLES ###################################
################################################################################

# User-modifiable variables
ADDRESS=192.168.139.106
PORT=1194
DNS=192.168.139.104
SUBNET=192.168.139.128
MASK=255.255.255.128
IFACE='eth0'

# Script static variables
CLIENT_TAR='/tmp/openvpn-client.tar.gz'
EASY_RSA='/etc/openvpn/.easy-rsa'
KEYS_DIR='/etc/openvpn/keys'

################################################################################
################################## UTILITIES ###################################
################################################################################

# Provides pretty colourful output with timestamps
output() {
  local LABEL='OpenVPN'
  local TIMESTAMP=$(date +%H:%M)
  local COLOUR='\033[34m' # Blue
  local RESET='\033[0m'   # Standard
  case $1 in
      ERROR) local COLOUR='\033[31m' ;; # Red
    SUCCESS) local COLOUR='\033[32m' ;; # Green
       WARN) local COLOUR='\033[33m' ;; # Yellow
  esac
  while read LINE; do
    echo -e "${COLOUR}${LABEL} [${TIMESTAMP}]${RESET} ${LINE}"
  done
}

# Produces bold output
say() {
  local BOLD=$(tput bold)
  local STD=$(tput sgr0)
  echo "${BOLD}$@${STD}"
}

# Creates a copy of $2 at $2.old
backup() {
  [[ -z $1 ]] && echo 'backup() - No name variable set' | output ERROR
  [[ -z $2 ]] && echo 'backup() - No file variable set' | output ERROR
  local NAME=$1
  local FILE=$2
  if [[ -f $FILE ]]; then
    echo "Backing up previous ${NAME} file..." | output
    RESULT=$(cp -f ${FILE} ${FILE}.old 2>&1)
    if [[ $? != 0 ]]; then
      echo "Failed to backup previous ${FILE} file!" | output WARN
      echo $RESULT | output WARN
    else
      echo "${NAME} backup created successfully" | output
    fi
  fi
}

# Just a pretty way of creating here documents, with error handling and backing
# up of the previous version.
createfile() {
  [[ -z $1 ]] && echo 'createfile() - No name variable set' | output ERROR
  [[ -z $2 ]] && echo 'createfile() - No file variable set' | output ERROR
  local NAME=$1
  local FILE=$2
  backup "$NAME" "$FILE"
  echo "Creating ${NAME}..." | output
  while read -r LINE; do
    # Add each line of STDIN to $CONTENT, along with a line break
    local CONTENT+="${LINE}\n"
  done
  RESULT=$(echo -e ${CONTENT} > ${FILE} 2>&1)
  if [[ $? != 0 ]]; then
    echo "Failed to create ${NAME} file!" | output ERROR
    echo $RESULT | output ERROR
    exit 1
  else
    echo "${NAME} file created successfully" | output
  fi
}

# Checks that the previous command exited correctly and quits the script if not,
# with a pretty error message. Optionally a second string can be provided to
# print on success.
onfail() {
  if [[ $? != 0 ]]; then
    echo $1 | output ERROR
  elif [[ ! -z $2 ]]; then
    echo $2 | output
  fi
}


################################################################################
################################# INSTALLATION #################################
################################################################################

say 'Installing RPM packages...' | output
yum install -e 0 -y openvpn           \
                    easy-rsa          \
                    iptables          \
                    iptables-utils    \
                    iptables-services | output
onfail 'Failed to install RPM packages!' 'RPM packages installed successfully'

say 'Setting up Easy-RSA...' | output
mkdir -p $EASY_RSA
  onfail "Failed to create Easy-RSA directory at ${EASY_RSA}"
cp -rf /usr/share/easy-rsa/2.0/* $EASY_RSA/
  onfail "Unable to copy Easy-RSA to $EASY_RSA"
cp -f $EASY_RSA/openssl-1.0.0.cnf $EASY_RSA/openssl.cnf
  onfail "Unable to create $EASY_RSA/openssl.cnf to force the OpenSSL version"
restorecon -R $EASY_RSA
  onfail "Unable to set SELinux context labels for ${EASY_RSA}"

################################################################################
################################ CONFIGURATION #################################
################################################################################

say 'Generating configuration files...' | output

# This is the main configuration file for OpenVPN and provides the core
# configuration parameters for running the service.
createfile 'OpenVPN server configuration' '/etc/openvpn/server.conf' <<OPENVPN
local $ADDRESS
port $PORT
proto udp
dev tun
comp-lzo
topology subnet
user nobody
group nobody
persist-key
persist-tun
ifconfig-pool-persist ipp.txt
keepalive 10 120
max-clients 100
status openvpn-status.log
log-append  openvpn.log
verb 3
mute 20

ca ${KEYS_DIR}/ca.crt
cert ${KEYS_DIR}/server.crt
key ${KEYS_DIR}/server.key
dh ${KEYS_DIR}/dh2048.pem
cipher AES-256-CBC
duplicate-cn
plugin /usr/lib64/openvpn/plugins/openvpn-plugin-auth-pam.so openvpn

server ${SUBNET} ${MASK}
push "route 192.168.139.0 255.255.255.128"
push "dhcp-option DNS $DNS"
OPENVPN

# The PAM configuration file permits access through the VPN to users with local
# POSIX accounts. Additional configuration can be added to only permit certain
# groups or users to authenticate using this method.
createfile 'OpenVPN PAM security configuration' '/etc/pam.d/openvpn' <<PAM
auth    required    pam_unix.so    shadow    nodelay
account required    pam_unix.so
PAM

# This minimal firewall configuration permits only SSH and OpenVPN connections
# as well as allowing SNAT connections through the VPN.
createfile 'Firewall rules' '/etc/sysconfig/iptables' <<IPTABLES
*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]

-A POSTROUTING -o $IFACE -j SNAT --to-source $ADDRESS
-A POSTROUTING -o $IFACE -j SNAT --to-source $ADDRESS
COMMIT

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A INPUT -i $IFACE -p udp -m state --state NEW -m udp --dport $PORT -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
IPTABLES

createfile 'Easy-RSA configuration' "${EASY_RSA}/vars" <<EASYRSA
export EASY_RSA="$EASY_RSA"
export OPENSSL="openssl"
export PKCS11TOOL="pkcs11-tool"
export GREP="grep"
export KEY_CONFIG=`$EASY_RSA/whichopensslcnf $EASY_RSA`
export KEY_DIR="$KEYS_DIR"
export PKCS11_MODULE_PATH="dummy"
export PKCS11_PIN="dummy"
export KEY_SIZE=2048
export CA_EXPIRE=3650
export KEY_EXPIRE=3650
export KEY_COUNTRY="GB"
export KEY_PROVINCE="DEVON"
export KEY_CITY="PLYMOUTH"
export KEY_ORG="Land Registry"
export KEY_EMAIL="webops@digital.landregistry.gov.uk"
export KEY_OU="IT Operations"
export KEY_NAME="server"
export KEY_CN="$(hostname)"
EASYRSA

createfile 'Client OpenVPN configuration' '/etc/openvpn/client.ovpn' <<CLIENT
client
dev tun
proto udp
remote $ADDRESS $PORT
resolv-retry infinite
remote-cert-tls server
ns-cert-type server
auth-nocache
auth-user-pass
nobind
persist-key
persist-tun
comp-lzo
verb 3
ca ca.crt
cert client.crt
key client.key
cipher AES-256-CBC
CLIENT

say 'Configuring kernel parameters...' | output
createfile 'Kernel parameters' '/etc/sysctl.d/openvpn' <<KERNEL
net.ipv4.ip_forward = 1
net.ipv4.conf.default.rp_filter = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.icmp_ignore_bogus_error_responses = 1
KERNEL
sysctl -p
  onfail 'Unable to set runtime parameters' 'Runtime parameters set'

################################################################################
################################### RUNTIME ####################################
################################################################################

say 'Creating authentication certificates...' | output
source $EASY_RSA/vars
  onfail "Failed to load Easy-RSA variables from ${EASY_RSA}/vars!"
bash $EASY_RSA/clean-all | output
  onfail "Failed to clean up ${KEYS_DIR}!"

echo 'Creating Diffie Hellman key... (this may take some time)' | output
bash $EASY_RSA/build-dh 2>/dev/null | output
  onfail 'Failed to create Diffie Hellman key!'

echo 'Creating Certificate Authority...' | output
bash $EASY_RSA/build-ca --batch 2>/dev/null | output
  onfail 'Failed to create Certificate Authority!'
echo 'Creating server-side certificate...' | output
bash $EASY_RSA/build-key-server --batch server 2>/dev/null | output
  onfail 'Failed to create server certificate!'
echo 'Creating client-side certificate...' | output
KEY_NAME="client" bash $EASY_RSA/build-key --batch client 2>/dev/null | output
  onfail 'Failed to create client certificate!'

restorecon -R ${KEYS_DIR}
  onfail "Unable to set SELinnux context labels for ${KEYS_DIR}"


say 'Reconfiguring SystemD network services...' | output
systemctl stop NetworkManager.service 2>&1 | output
  onfail 'Failed to stop NetworkManager.service!'
systemctl stop firewalld.service 2>&1 | output
  onfail 'Failed to stop firewalld.service!'
systemctl start iptables.service 2>&1 | output
  onfail 'Failed to start iptables.service'
systemctl restart network.service 2>&1 | output
  onfail 'Failed to restart network.service'
systemctl enable iptables.service >/dev/null 2>&1
systemctl disable firewalld.service >/dev/null 2>&1
systemctl disable NetworkManager.service >/dev/null 2>&1


say 'Starting OpenVPN service...' | output
systemctl stop openvpn@server.service 2>&1 | output
systemctl start openvpn@server.service 2>&1 | output
  onfail 'Failed to start OpenVPN service'
systemctl enable openvpn@server.service >/dev/null 2>&1


say 'Packaging client configuration...' | output
TMP_DIR="/tmp/$(openssl rand -hex 6)"
mkdir -p $TMP_DIR
  onfail "Unable to create temporary directory at $TMP_DIR"
cp $KEYS_DIR/{ca.crt,client.crt,client.key} $TMP_DIR
  onfail "Unable to copy necessary certificates to $TMP_DIR"
cp /etc/openvpn/client.ovpn $TMP_DIR
  onfail "Unable to copy client configuration to $TMP_DIR"
tar -C $TMP_DIR -caf $CLIENT_TAR .
  onfail "Unable to create compressed archive at $CLIENT_TAR"
rm -rf $TMP_DIR
echo "Client configuration can be found at $CLIENT_TAR" | output
[[ -d '/vagrant' ]] && cp -f $CLIENT_TAR /vagrant

say 'Installation complete!' | output SUCCESS