#!/bin/bash -e
#
# freeipa-letsencrypt.sh - script to setup Let's Encrypt's Certbot for FreeIPA
#
# Version 1.0, latest version, documentation and bugtracker available at:
#		https://gitlab.lindenaar.net/scripts/freeipa
#
# Copyright (c) 2018 Frederik Lindenaar
#
# This script is free software: you can redistribute and/or modify it under the
# terms of version 3 of the GNU General Public License as published by the Free
# Software Foundation, or (at your option) any later version of the license.
#
# This script is distributed in the hope that it will be useful but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# this program.  If not, visit <http://www.gnu.org/licenses/> to download it.

# Sanity checks, ensure we have a valid Kerberos ticket, current host is a
# FreeIPA server, certbot is installed and that we can run priviliged commands
die() { echo $* >&2; exit 1; }
if ! klist -s; then
    die no valid Kerberos ticket, please login to FreeIPA using kinit first
elif ! ipa server-show ${HOSTNAME:=$(hostname --fqdn)} > /dev/null; then
    die this script should be run on an active IPA server
elif ! which certbot > /dev/null; then
    die this script requires Certbot to be installed, please install that first
elif [ $(id -u) == 0 ]; then
    unset SUDO
elif ! ${SUDO:=sudo} -v; then
    die Error: this script must be run by root and $SUDO does not seem to work
else
    $SUDO kinit -k
fi

# Set KRB5CCNAME to ensure the current ticket cache will be used
: ${KRB5CCNAME:=$(klist -l | head -3 | tail -1 | cut -d\  -f2-)}

# Set parameters
: ${CERTNAME:=$(ipa host-show $HOSTNAME --raw | fgrep "krbcanonicalname: host/" | cut -d/ -f2 | cut -d@ -f1)}
: ${DNSALTNAMES:=$(ipa host-show $HOSTNAME --raw | fgrep "krbprincipalname: host/" | cut -d/ -f2 | cut -d@ -f1 | paste -sd,)}
: ${EMAIL:=hostmaster@${HOSTNAME#*.}}
: ${SERVICE:=letsencrypt/$(ipa host-show $HOSTNAME --raw | fgrep "krbcanonicalname: host/" | cut -d/ -f2)}

# Ensure the user consents with changing his system.
if tty > /dev/null; then
    cat << EOT
This script modifies this host's FreeIPA setup so that its web interface will
use a Let's Encrypt certificate and will automatically renew that when needed.
The following changes will be made for this:
  1. Add Let's Encrypt Root and Intermediate CAs as trusted CAs
  2. Create DNS Administrator role in FreeIPA that can edit any DNS Record
  3. Create host service: $SERVICE
  4. Allow letsencrypt host service to manage DNS entries
  5. Register with Let's encrypt as: $EMAIL
  6. Request a Let's Encrypt SSL certificate for: $CERTNAME
     with DNS Alternative names: $DNSALTNAMES
  7. install the Let's Encrypt certificate in apache as host SSL certificate,
     storing renewal config in: /etc/letsencrypt/renewal/$HOSTNAME.conf
  8. configure the Fedora Certbot renew timer so that certbot is run daily to
     renew the certificate when needed.
EOT
    while ! [[ "${REPLY:-}" =~ ^[YyNn]$ ]]; do
        echo
        read -rp "Please confirm these changes should be applied (y/n): " -n 1
    done
    echo
    [[ "${REPLY}" =~ ^[Nn]$ ]] && die aborted
fi

echo
echo Download and importing Let\'s Encrypt certificates, this may take a while
declare -A LETSENCRYPTCERTS=(
    [ISRGRootCAX1]=https://letsencrypt.org/certs/isrgrootx1.pem
    [LetsEncryptX3]=https://letsencrypt.org/certs/letsencryptauthorityx3.pem
)
for certname in ${!LETSENCRYPTCERTS[@]}; do
    certfile=$(mktemp -u ${TMPDIR:-/tmp}/$0.XXXXXXX.cert)
    curl -s "${LETSENCRYPTCERTS[$certname]}" -o $certfile
    $SUDO ipa-cacert-manage install $certfile -n "$certname" -t C,,
    rm -f $certfile
done
$SUDO ipa-certupdate

echo
if ! ipa role-show "DNS Administrator" > /dev/null 2>&1; then
    echo Creating DNS Administrator role
    ipa role-add "DNS Administrator"
    ipa role-add-privilege "DNS Administrator" --privileges="DNS Administrators"
else
    echo DNS Administrator role already exists
fi

echo
if ! ipa service-show "$SERVICE" > /dev/null 2>&1; then
    echo Add service user $SERVICE
    ipa service-add "$SERVICE"
    ipa role-add-member "DNS Administrator" --services="$SERVICE"
else
    echo Service user $SERVICE already exists
fi

echo
if [ ! -f "${KEYTAB:=/etc/letsencrypt/keytab}" ]; then
    echo creating keytab file $KEYTAB
    $SUDO ipa-getkeytab -p "$SERVICE" -k "$KEYTAB"
else
    echo not touching existing keytab file $KEYTAB
fi

echo
echo Requesting Let\'s Encrypt SSL certificate and setup renewals
$SUDO certbot certonly --expand --manual --preferred-challenges dns \
        --manual-public-ip-logging-ok --agree-tos --email "${EMAIL}" \
        --cert-name ${HOSTNAME} --domains "${DNSALTNAMES}" \
        --pre-hook "kinit -k -t $KEYTAB \"$SERVICE\"" --post-hook "kdestroy" \
        --manual-auth-hook    "ipa dnsrecord-add ${DOMAIN:-\${CERTBOT_DOMAIN#*.\}}. _acme-challenge.\${CERTBOT_DOMAIN}. \"--txt-rec=\${CERTBOT_VALIDATION}\"; sleep 3" \
        --manual-cleanup-hook "ipa dnsrecord-del ${DOMAIN:-\${CERTBOT_DOMAIN#*.\}}. _acme-challenge.\${CERTBOT_DOMAIN}. --del-all" \
        --deploy-hook  'echo | ipa-server-certinstall --http "${RENEWED_LINEAGE}/fullchain.pem" "${RENEWED_LINEAGE}/privkey.pem" --dirman-password="" --pin="" && service httpd restart'

echo
echo Enabling Certbot package\'s renewal timer
$SUDO systemctl enable --now certbot-renew.timer

cat << EOT

FreeIPA was successfully setup to use a Let's Encrypt certificate for its web
interface. This certificate will be renewed automatically when needed.

EOT