acme-client 30 dec 2016 | Last updated: 18 jan 2017 00:00



This should be the final and my definitive guide on using Let's Encrypt and acme-client on FreeBSD. I've written multiple posts about this but things have changed again. I believe that the LetsEncrypt service is now stable and the acme-client seems to be stable as well.

acme-client

If you just want to dig in, jump to the Install acme-client chapter.

  1. My first guide used the official Let's Encrypt python client (now known as CertBot). I found that to be way too fat and had too many dependencies to be allowed to run as root.
  2. My second guide used Lukas Schauer's LetsEncrypt.sh client (now known as Dehydrated) which only required openssl and either bash or zsh. This is still a good method as it has separated privileged and un-privileged actions.
  3. My third guide used Kristaps Dzonsons' LetskEncrypt client (now known as acme-client).
  4. This latest guide uses acme-client which is the new name for LetskEncrypt.

acme-client is a client for Let's Encrypt users, but one designed for security. No Python. No Ruby. No Bash. A straightforward, open source implementation in C that isolates each step of the sequence.

The acme-client process will be started by root but drops privileges to nobody and chroot's any action that does not require root privileges. It must run as root to be able to drop privileges and run as an unprivileged user.

As a proponent of LibreSSL I can't let solutions that use libtls from LibreSSL pass by without trying to use them. I'm the creator and maintainer of the security/acme-client port in the FreeBSD ports tree.

Recent changes

The acme-client is now a part of the OpenBSD base system in addition to being a portable project for other operating systems.

Trademark & name change

In June 2016, the LetsEncrypt project noticed that Comodo, a provider of SSL certificates, was trying to hijack the "Let's Encrypt" trademark. After the LetsEncrypt project managed to establish its rightful ownership of the trademark, Comodo dropped the trademark claims. As a side-effect the official LetsEncrypt client was renamed to CertBot and all other projects using the LetsEncrypt name had to be renamed.

The LetskEncrypt process was quick off the bat and snapped the acme-client name.

Instructions to migrate from the old LetskEncrypt to the new acme-client directory-structure is documented in /usr/ports/UPDATING and the pkg-message.

acme-client changes

A new feature -b was added which makes a backup of the old key when it is renewed.

Port changes

The port as of version 0.1.15 no longer requires the user to switch to LibreSSL completely. By default it will check if LibreSSL is the default provider for libcrypto and libssl (SSL_DEFAULT=libressl). The port will build LibreSSL but not install it and statically link the not-installed libraries.

For users that have fully switched to LibreSSL there's no difference.

Install acme-client

The port is available in the ports tree. Install it using the official pkg repository using

pkg install acme-client

or alternatively build your own using Poudriere or any of the other building-from-source options and install it.

Configuration will land in /usr/local/etc/acme. The keys, certificates and certificate-chains will be stored in /usr/local/etc/ssl/acme by default. You should want to check that the configuration directory is not world-writable. The default directories in /usr/local/etc/ssl will be created with sane access restrictions when you install the port or package.

/usr/local/etc/
    acme/
    ssl/
    ssl/certs
    ssl/private

Prepare directories

To make life easier all of the challenges (LetsEncrypt as well as keybase etc) will be hosted in a shared dir /usr/local/www/.well-known on the jail running my Apache server.

mkdir -pm750 /usr/jails/http/usr/local/www/.well-known

The LetsEncrypt and acme-client bits will land in /usr/local/etc/acme, the private keys will land in /usr/local/etc/ssl/private and certificates will land in domain-specific directories in /usr/local/etc/ssl/acme on the host system. These directories are created by the port/package upon installation apart from the domain-specific certificate directories.

Modify web-server configuration

The acme validation will GET a uniquely named file from http://<example.org>/.well-known/acme-challenge/ directory.

Apache

Access to the .well-known directory is granted in my main Apache config file /usr/local/etc/apache24/httpd.conf

httpd.conf

<Directory "/usr/local/www/.well-known/">
   Options None
   AllowOverride None
   Require all granted
   Header add Content-Type text/plain
</Directory>

If you want to only share the ACME challenges you can suffix .well-known/ with acme-challenge/

Now every (non-ssl) Virtual Host that I have gets a on-line addition

vhosts/domain.conf

Alias /.well-known/ /usr/local/www/.well-known/

nginx

You'll need to add the following to the top of your location matches so requests from LetsEncrypt's acme servers get the correct responses.

 # Letsencrypt needs http for acme challenges
 location ^~ /.well-known/acme-challenge/ {
     proxy_redirect off;
     default_type "text/plain";
     root /usr/local/www/.well-known/acme-challenge ;
     allow all;
 }

acme-client configuration

acme-client works different from the other clients I've used as it does not use configuration files. Everything is handled passing parameters with values to the command. The intended use-case is a system that hosts a single domain.

Domains to sign

The script requires a list of domain names you want to have a SAN cert for in the following format:

example.com www.example.com
example.net www.example.net wiki.example.net

Domains and sub-domains that are listed on the ''same line'' will result in SAN-certificates (Subject-Alternative-Name).
Store this as /usr/local/etc/letsencrypt/domains.txt

!!! caution Make sure the first item in every line of domains.txt is unique or you'll end up in a real mess!

The renew script

The script tries to make sure all things that need to exist actually do exist. Some of the statements are "on-off", after first run they can be deleted.

/usr/local/etc/acme/acme-client.sh

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#!/bin/sh -e

# Define location of dirs and files
DOMAINSFILE="/usr/local/etc/acme/domains.txt"
CHALLENGEDIR="/usr/jails/http/usr/local/www/.well-known/acme-challenge"
SSLDIR="/usr/local/etc/ssl"

# Check for account key and create dir and key (-n) if required
if [ ! -f "/usr/local/etc/acme/privkey.pem" ] ; then
   EXTRAARGS="${EXTRAARGS} -n"
fi

# Loop through the domains.txt file with lines like
# example.org www.example.org img.example.org
cat ${DOMAINSFILE} | while read domain subdomains ; do
   # Set the directory where cert.pem, fullchain.pem and chain.pem are saved
   CERTDIR="${SSLDIR}/${domain}"
   # Define the name of the private key
   DOMAINKEY="${SSLDIR}/priv/${domain}.pem"
   # Make sure the certificates can be stored for this domain
   mkdir -pm755 "${CERTSDIR}" 2>/dev/null

   # acme-client returns RC=2 when certificates weren't changed
   set +e
   # Renew the key and certs if required
   acme-client -b -C "${CHALLENGEDIR}" \
               -k "${DOMAINKEY}" \
               -c "${CERTDIR}" \
               ${EXTRAARGS} \
               ${domain} ${subdomains}
   RC=$?
   set -e
   [ $RC -ne 2 ] && exit 1
done

In-line configuration

If you don't want to use a domains.txt configuration file you can use a different construct to include the list in your /usr/local/etc/letsencrypt/letskencrypt.sh script (changed lines only).

...
while read domain line ; do
...
done <<ENDOFLIST
example.com www.example.com
example.net www.example.net wiki.example.net
ENDOFLIST

Configure periodic job

The FreeBSD port contains a periodic(8) script for full automation of your certificate renewal. The periodic script allows using a script for renewals or periodic variables only for a single key/certifcate

Using the domains.txt file

To setup periodic to use the script

/etc/periodic.conf

weekly_acme_client_enable="YES"
weekly_acme_client_renewscript="/usr/local/etc/acme/acme-client.sh"
weekly_acme_client_deployscript="/usr/local/etc/acme/deploy.sh"

Obviously you can also add your deployment to the renewal script if you would like to.

Using periodic.conf for a single cert

If you have only one certificate to renew on the machine, then you do so without a script by using periodic variables

/etc/periodic.conf

weekly_acme_client_enable="YES"
weekly_acme_client_domains="example.com www.example.com example.net www.example.net"
weekly_acme_client_challengedir="/usr/jails/http/usr/local/www/.well-known/acme-challenge"
weekly_acme_client_args="-c /usr/jails/http/usr/local/ssl/certs -p /usr/jails/http/usr/local/ssl/priv"

In stead of using the weekly_acme_client_args you can also use weekly_acme_client_deployscript for your single certificate deployment.

You will have to take care of creating the Account Key first time yourself!

The remainder of this guide assumes you use the weekly_acme_client_renewscript method.

First run

You will probably want to run your LetsEncrypt manually the first time (as root) after you've setup periodic

/usr/local/etc/periodic/weekly/000.acme-client.sh

You will end up with a sub-directory certs that contains your domains as directories with the Subject-Alternative-Names certs and the corresponding private keys in the priv sub-directory.

/usr/local/etc/ssl/
   example.com/
      cert.pem
      chain.pem
      fullchain.pem
   priv/example.com.pem
   example.net/
      cert.pem
      chain.pem
      fullchain.pem
   priv/example.net.pem

Deploy new certs

The port contains a script (/usr/local/etc/acme/deploy.sh) that you can adapt to your needs.

Here you'll probably need to get creative with scripting. In the host environment, you now have

/usr/local/etc/ssl/priv/example.net.pem
/usr/local/etc/ssl/example.net/fullchain.pem

Example (jailed) applications

Your Apache server may (should?) run in the http jail and you've setup an Apache Virtual Host with

SSLCertificateFile /etc/ssl/certs/example.net.pem
SSLCertificateKeyFile /etc/ssl/priv/example.net.pem

and your OpenSMTPd mailserver for example.net in the mail jail

pki example.net certificate "/etc/ssl/certs/example.net.pem"
pki example.net key         "/etc/ssl/priv/example.net.pem"
listen on $lan_addr port 587 tls-require \
       pki example.net hostname example.net auth

Seen from the host environment your certificates actually need to end up in

/usr/jails/http/etc/ssl
/usr/jails/mail/etc/ssl

NB: Some applications want the certificate and chain as separate files. If this is the case you'll need to copy cert.pem and chain.pem to the appropriate location in stead.

Example deploy script

I've extended the default script. There's sufficient room to add your own domains.

Since acme-client runs as root you don't need to separate the renew and deploy scripts, you could make combine these.

/usr/local/etc/acme/seploy.sh :::sh #!/bin/sh -e

DOMAINSFILE="/usr/local/etc/acme/domains.txt"
SSLDIR="/usr/local/etc/ssl"
JAILSDIR="/usr/jails"

cat ${DOMAINSFILE} | while read domain subdomains ; do

   case ${domain} in
      mta.example.net) targetjails=mail ;;
      *)               targetjails=http ;;
   esac

   for jail in ${targetjails}; do
      targetdir="${JAILSDIR}/${jail}/etc/ssl"
      # Skip to next if cert hasn't changed
      [ -z "`diff -rq ${SSLDIR}/certs/${domain}/fullchain.pem ${targetdir}/certs/${domain}.pem`" ] && continue
      cp "${SSLDIR}/private/${domain}.pem"   "${targetdir}/priv/${domain}.pem"
      cp "${SSLDIR}/${domain}/fullchain.pem" "${targetdir}/certs/${domain}.pem"
      chmod 400 "${targetdir}/priv/${domain}.pem"
      chmod 644 "${targetdir}/certs/${domain}.pem"
      # Mark jail/service for restart/-load
      eval restart${jail}=yes
   done

done

# Restart services when marked
[ -n "${restarthttp}" ] && jexec http service apache24 restart
[ -n "${restartmail}" ] && jexec mail service smtpd restart

Example output of successful invocation with -v

acme-client: https://acme-v01.api.letsencrypt.org/directory: directories
acme-client: acme-v01.api.letsencrypt.org: DNS: 104.98.130.119
acme-client: https://acme-v01.api.letsencrypt.org/acme/new-authz: req-auth: example.org
acme-client: https://acme-v01.api.letsencrypt.org/acme/new-authz: req-auth: www.example.org
acme-client: /jails/http/usr/local/www/.well-known/acme-challenge/<snip>: created
acme-client: https://acme-v01.api.letsencrypt.org/acme/challenge/<snip>/<snip>: challenge
acme-client: /jails/http/usr/local/www/.well-known/acme-challenge/<snip>: created
acme-client: https://acme-v01.api.letsencrypt.org/acme/challenge/<snip>/<snip>: challenge
acme-client: https://acme-v01.api.letsencrypt.org/acme/challenge/<snip>/<snip>: status
acme-client: https://acme-v01.api.letsencrypt.org/acme/challenge/<snip>/<snip>: status
acme-client: https://acme-v01.api.letsencrypt.org/acme/new-cert: certificate
acme-client: http://cert.int-x3.letsencrypt.org/: full chain
acme-client: cert.int-x3.letsencrypt.org: DNS: 185.27.16.17
acme-client: /usr/local/etc/ssl/certs/example.org/chain.pem: created
acme-client: /usr/local/etc/ssl/certs/example.org/cert.pem: created
acme-client: /usr/local/etc/ssl/certs/example.org/fullchain.pem: created