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Bash shell script to Distribute Let's Encrypt Keys on LAN

Usage - Most Cases through Crontab

Put this in either root or system crontab to run every 12 hours (See below)

Assumptions of script:

  • SSL Certs are obtained through Let's Encrypt
  • This script will grab the fullchain.pem file from the LAN host where Let's Encrypt certificates are stored and renewed. On the LAN host - after updating the LE certs, the fullchain.pem is copied to an apache accessible directory via a --deploy-hook script for distribution of the SSL certificates for servers requiring these on the LAN. This deploy hook could be run with the ACME client such as certbot. An Apache <Virtual Host> configuration restricts access of this file to IP addresses on the Local LAN
  • The fullchain.pem file is not secret in that it is normally read and passed in headers during the normal SSL handshake
  • The script also assumes the the privkey.pem has previously been distributed through other means since this key is secret. This script will check for presence of privkey.pem and will exit if key is not found. The privkey.pem file should not change with LE certification renewal since certs are renewed with --reuse-key option that reuses the private key.
  • Depending on the application, this script could gracefully restart apache web server or a different systemd/rc service (rc service on BSD or systemctl service on Linux).
  • The script should work on Linux/BSD operating systems

deploy-hook script:

(This is called usually from certbot with the --reuse-key option) i.e.certbot certonly --cert-name example.com -d example.com,domain1.example.com,domain2.example.com,www.example.com,domain3.example.com --dns-cloudflare --dns-cloudflare-credentials /usr/local/etc/letsencrypt/cloudflare_used_by_certbot.ini --reuse-key --deploy-hook /root/bin/renew.sh

#!/usr/bin/env bash
#renew.sh
set -e
for domain in $RENEWED_DOMAINS; do
   # Just an example, you can use any non-sensitive storage medium you want
  cp -rL "$RENEWED_LINEAGE/fullchain.pem" /usr/local/www/main/certs/
  
  SHA256SUM=$(trim "$(openssl dgst -sha256 "${WebDirectoryDestination}/${FullChainFile}" | cut -d"=" -f2)")
  echo "Creating SHA256 digest for ${FullChainFile}"
  printf "%s" "${SHA256SUM}" > "${WebDirectoryDestination}/${FullChainFile}.sha256"
done

Example Apache <Virtual Host> directive that would limit access to fullchain.pem file to LAN

   <Directory /usr/local/www/main/certs>
        Require all denied
        Options -Indexes
        <RequireAll>
              Require ip 10.0.1.0/24
        </RequireAll>
   </Directory>

Further Explanation

PATH=/sbin:/bin:/usr/bin:/usr/local/bin
0 */12 * * * python2.7 -c 'import random; import time; time.sleep(random.random() * 3600)' && certbot renew --cert-name example.com --reuse-key  --dns-cloudflare --dns-cloudflare-credentials /usr/local/etc/letsencrypt/cloudflare_used_by_certbot.ini --deploy-hook /root/bin/renew.sh
  • Every LAN Machine that requires use of certificates (i.e. Internal Apache Server, Xen Orchestra Server, pfSense) would run this script through a root cronjob every 12 hours to update the fullchain.pem file. The privkey.pem file is not distributed with this script and it's assumed this file already installed on each LAN machine requiring a copy of the fullchain.pem certificate.
PATH=/sbin:/bin:/usr/bin:/usr/local/bin
0 */12 * * * bash <this-script.sh>

References:

https://community.letsencrypt.org/t/automated-deployment-of-key-cert-from-reverse-proxy-to-internal-systems/64491/4 https://gist.github.com/onnimonni/b49779ebc96216771a6be3de46449fa1