···
+
<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="module-security-acme">
+
<title>SSL/TLS Certificates with ACME</title>
+
NixOS supports automatic domain validation & certificate
+
retrieval and renewal using the ACME protocol. Any provider can be
+
used, but by default NixOS uses Let's Encrypt. The alternative ACME
+
<link xlink:href="https://go-acme.github.io/lego/">lego</link> is
+
Automatic cert validation and configuration for Apache and Nginx
+
virtual hosts is included in NixOS, however if you would like to
+
generate a wildcard cert or you are not using a web server you will
+
have to configure DNS based validation.
+
<section xml:id="module-security-acme-prerequisites">
+
<title>Prerequisites</title>
+
To use the ACME module, you must accept the provider's terms of
+
<xref linkend="opt-security.acme.acceptTerms"></xref> to
+
<literal>true</literal>. The Let's Encrypt ToS can be found
+
<link xlink:href="https://letsencrypt.org/repository/">here</link>.
+
You must also set an email address to be used when creating
+
accounts with Let's Encrypt. You can set this for all certs with
+
<xref linkend="opt-security.acme.defaults.email"></xref> and/or on
+
<xref linkend="opt-security.acme.certs._name_.email"></xref>. This
+
address is only used for registration and renewal reminders, and
+
cannot be used to administer the certificates in any way.
+
Alternatively, you can use a different ACME server by changing the
+
<xref linkend="opt-security.acme.defaults.server"></xref> option
+
to a provider of your choosing, or just change the server for one
+
<xref linkend="opt-security.acme.certs._name_.server"></xref>.
+
You will need an HTTP server or DNS server for verification. For
+
HTTP, the server must have a webroot defined that can serve
+
<filename>.well-known/acme-challenge</filename>. This directory
+
must be writeable by the user that will run the ACME client. For
+
DNS, you must set up credentials with your provider/server for use
+
<section xml:id="module-security-acme-nginx">
+
<title>Using ACME certificates in Nginx</title>
+
NixOS supports fetching ACME certificates for you by setting
+
<literal>enableACME = true;</literal> in a virtualHost config. We
+
first create self-signed placeholder certificates in place of the
+
real ACME certs. The placeholder certs are overwritten when the
+
ACME certs arrive. For <literal>foo.example.com</literal> the
+
config would look like this:
security.acme.acceptTerms = true;
+
security.acme.defaults.email = "admin+acme@example.com";
+
"foo.example.com" = {
# All serverAliases will be added as extra domain names on the certificate.
+
serverAliases = [ "bar.example.com" ];
+
locations."/" = {
+
root = "/var/www";
# We can also add a different vhost and reuse the same certificate
# but we have to append extraDomainNames manually beforehand:
+
# security.acme.certs."foo.example.com".extraDomainNames = [ "baz.example.com" ];
+
"baz.example.com" = {
+
useACMEHost = "foo.example.com";
+
locations."/" = {
+
root = "/var/www";
+
<section xml:id="module-security-acme-httpd">
+
<title>Using ACME certificates in Apache/httpd</title>
+
Using ACME certificates with Apache virtual hosts is identical to
+
using them with Nginx. The attribute names are all the same, just
+
replace "nginx" with "httpd" where
+
<section xml:id="module-security-acme-configuring">
+
<title>Manual configuration of HTTP-01 validation</title>
+
First off you will need to set up a virtual host to serve the
+
challenges. This example uses a vhost called
+
<literal>certs.example.com</literal>, with the intent that you
+
will generate certs for all your vhosts and redirect everyone to
security.acme.acceptTerms = true;
+
security.acme.defaults.email = "admin+acme@example.com";
# /var/lib/acme/.challenges must be writable by the ACME user
# and readable by the Nginx user. The easiest way to achieve
# this is to add the Nginx user to the ACME group.
+
users.users.nginx.extraGroups = [ "acme" ];
+
"acmechallenge.example.com" = {
# Catchall vhost, will redirect users to HTTPS for all vhosts
+
serverAliases = [ "*.example.com" ];
+
locations."/.well-known/acme-challenge" = {
+
root = "/var/lib/acme/.challenges";
+
locations."/" = {
+
return = "301 https://$host$request_uri";
# Alternative config for Apache
+
users.users.wwwrun.extraGroups = [ "acme" ];
+
"acmechallenge.example.com" = {
# Catchall vhost, will redirect users to HTTPS for all vhosts
+
serverAliases = [ "*.example.com" ];
# /var/lib/acme/.challenges must be writable by the ACME user and readable by the Apache user.
# By default, this is the case.
+
documentRoot = "/var/lib/acme/.challenges";
···
+
Now you need to configure ACME to generate a certificate.
+
security.acme.certs."foo.example.com" = {
+
webroot = "/var/lib/acme/.challenges";
+
email = "foo@example.com";
# Ensure that the web server you use can read the generated certs
# Take a look at the group option for the web server you choose.
+
group = "nginx";
# Since we have a wildcard vhost to handle port 80,
# we can generate certs for anything!
# Just make sure your DNS resolves them.
+
extraDomainNames = [ "mail.example.com" ];
+
The private key <filename>key.pem</filename> and certificate
+
<filename>fullchain.pem</filename> will be put into
+
<filename>/var/lib/acme/foo.example.com</filename>.
+
Refer to <xref linkend="ch-options"></xref> for all available
+
configuration options for the
+
<link linkend="opt-security.acme.certs">security.acme</link>
+
<section xml:id="module-security-acme-config-dns">
+
<title>Configuring ACME for DNS validation</title>
+
This is useful if you want to generate a wildcard certificate,
+
since ACME servers will only hand out wildcard certs over DNS
+
validation. There are a number of supported DNS providers and
+
servers you can utilise, see the
+
<link xlink:href="https://go-acme.github.io/lego/dns/">lego
+
docs</link> for provider/server specific configuration values. For
+
the sake of these docs, we will provide a fully self-hosted
+
include "/var/lib/secrets/dnskeys.conf";
+
name = "example.com";
+
file = "/var/db/bind/${name}";
+
extraConfig = "allow-update { key rfc2136key.example.com.; };";
# Now we can configure ACME
security.acme.acceptTerms = true;
+
security.acme.defaults.email = "admin+acme@example.com";
+
security.acme.certs."example.com" = {
+
domain = "*.example.com";
+
dnsProvider = "rfc2136";
+
credentialsFile = "/var/lib/secrets/certs.secret";
# We don't need to wait for propagation since this is a local DNS server
dnsPropagationCheck = false;
+
The <filename>dnskeys.conf</filename> and
+
<filename>certs.secret</filename> must be kept secure and thus you
+
should not keep their contents in your Nix config. Instead,
+
generate them one time with a systemd service:
systemd.services.dns-rfc2136-conf = {
+
requiredBy = ["acme-example.com.service" "bind.service"];
+
before = ["acme-example.com.service" "bind.service"];
+
ConditionPathExists = "!/var/lib/secrets/dnskeys.conf";
+
Type = "oneshot";
···
chmod 400 /var/lib/secrets/dnskeys.conf
# extract secret value from the dnskeys.conf
+
while read x y; do if [ "$x" = "secret" ]; then secret="''${y:1:''${#y}-3}"; fi; done < /var/lib/secrets/dnskeys.conf
cat > /var/lib/secrets/certs.secret << EOF
RFC2136_NAMESERVER='127.0.0.1:53'
···
+
Now you're all set to generate certs! You should monitor the first
+
<literal>systemctl start acme-example.com.service & journalctl -fu acme-example.com.service</literal>
+
and watching its log output.
+
<section xml:id="module-security-acme-config-dns-with-vhosts">
+
<title>Using DNS validation with web server virtual hosts</title>
+
It is possible to use DNS-01 validation with all certificates,
+
including those automatically configured via the Nginx/Apache
+
<link linkend="opt-services.nginx.virtualHosts._name_.enableACME"><literal>enableACME</literal></link>
+
option. This configuration pattern is fully supported and part of
+
the module's test suite for Nginx + Apache.
+
You must follow the guide above on configuring DNS-01 validation
+
first, however instead of setting the options for one certificate
+
<xref linkend="opt-security.acme.certs._name_.dnsProvider"></xref>)
+
you will set them as defaults (e.g.
+
<xref linkend="opt-security.acme.defaults.dnsProvider"></xref>).
# Configure ACME appropriately
security.acme.acceptTerms = true;
+
security.acme.defaults.email = "admin+acme@example.com";
security.acme.defaults = {
+
dnsProvider = "rfc2136";
+
credentialsFile = "/var/lib/secrets/certs.secret";
# We don't need to wait for propagation since this is a local DNS server
dnsPropagationCheck = false;
···
+
"foo.example.com" = {
+
And that's it! Next time your configuration is rebuilt, or when
+
you add a new virtualHost, it will be DNS-01 validated.
+
<section xml:id="module-security-acme-root-owned">
+
<title>Using ACME with services demanding root owned
+
Some services refuse to start if the configured certificate files
+
are not owned by root. PostgreSQL and OpenSMTPD are examples of
+
these. There is no way to change the user the ACME module uses (it
+
will always be <literal>acme</literal>), however you can use
+
systemd's <literal>LoadCredential</literal> feature to resolve
+
this elegantly. Below is an example configuration for OpenSMTPD,
+
but this pattern can be applied to any service.
# Configure ACME however you like (DNS or HTTP validation), adding
# the following configuration for the relevant certificate.
# Note: You cannot use `systemctl reload` here as that would mean
# the LoadCredential configuration below would be skipped and
# the service would continue to use old certificates.
+
security.acme.certs."mail.example.com".postRun = ''
systemctl restart opensmtpd
# Now you must augment OpenSMTPD's systemd service to load
+
systemd.services.opensmtpd.requires = ["acme-finished-mail.example.com.target"];
systemd.services.opensmtpd.serviceConfig.LoadCredential = let
+
certDir = config.security.acme.certs."mail.example.com".directory;
+
"cert.pem:${certDir}/cert.pem"
+
"key.pem:${certDir}/key.pem"
# Finally, configure OpenSMTPD to use these certs.
+
credsDir = "/run/credentials/opensmtpd.service";
+
pki mail.example.com cert "${credsDir}/cert.pem"
+
pki mail.example.com key "${credsDir}/key.pem"
listen on localhost tls pki mail.example.com
action act1 relay host smtp://127.0.0.1:10027
match for local action act1
+
<section xml:id="module-security-acme-regenerate">
+
<title>Regenerating certificates</title>
+
Should you need to regenerate a particular certificate in a hurry,
+
such as when a vulnerability is found in Let's Encrypt, there is
+
now a convenient mechanism for doing so. Running
+
<literal>systemctl clean --what=state acme-example.com.service</literal>
+
will remove all certificate files and the account data for the
+
given domain, allowing you to then
+
<literal>systemctl start acme-example.com.service</literal> to
+
<section xml:id="module-security-acme-fix-jws">
+
<title>Fixing JWS Verification error</title>
+
It is possible that your account credentials file may become
+
corrupt and need to be regenerated. In this scenario lego will
+
produce the error <literal>JWS verification error</literal>. The
+
solution is to simply delete the associated accounts file and
+
re-run the affected service(s).
# Find the accounts folder for the certificate
systemctl cat acme-example.com.service | grep -Po 'accounts/[^:]*'
+
export accountdir="$(!!)"
# Move this folder to some place else
mv /var/lib/acme/.lego/$accountdir{,.bak}
# Recreate the folder using systemd-tmpfiles
···
# Note: Do this for all certs that share the same account email address
systemctl start acme-example.com.service
pyrox.dev