nixpkgs/nixos/modules/security/acme.xml

<chapter xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xmlns:xi="http://www.w3.org/2001/XInclude"
         version="5.0"
         xml:id="module-security-acme">
 <title>SSL/TLS Certificates with ACME</title>
 <para>
  NixOS supports automatic domain validation &amp; certificate retrieval and
  renewal using the ACME protocol. Any provider can be used, but by default
  NixOS uses Let's Encrypt. The alternative ACME client <literal>lego</literal>
  is used under the hood.
 </para>
 <para>
  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.
 </para>
 <section xml:id="module-security-acme-prerequisites">
  <title>Prerequisites</title>

  <para>
   To use the ACME module, you must accept the provider's terms of service
   by setting <literal><xref linkend="opt-security.acme.acceptTerms" /></literal>
   to <literal>true</literal>. The Let's Encrypt ToS can be found
   <link xlink:href="https://letsencrypt.org/repository/">here</link>.
  </para>

  <para>
   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
   <literal><xref linkend="opt-security.acme.email" /></literal>
   and/or on a per-cert basis with
   <literal><xref linkend="opt-security.acme.certs._name_.email" /></literal>.
   This address is only used for registration and renewal reminders,
   and cannot be used to administer the certificates in any way.
  </para>

  <para>
   Alternatively, you can use a different ACME server by changing the
   <literal><xref linkend="opt-security.acme.server" /></literal> option
   to a provider of your choosing, or just change the server for one cert with
   <literal><xref linkend="opt-security.acme.certs._name_.server" /></literal>.
  </para>

  <para>
   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 with lego.
  </para>
 </section>
 <section xml:id="module-security-acme-nginx">
  <title>Using ACME certificates in Nginx</title>

  <para>
   NixOS supports fetching ACME certificates for you by setting
   <literal><link linkend="opt-services.nginx.virtualHosts._name_.enableACME">enableACME</link>
   = 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.
  </para>

<programlisting>
<xref linkend="opt-security.acme.acceptTerms" /> = true;
<xref linkend="opt-security.acme.email" /> = "admin+acme@example.com";
services.nginx = {
  <link linkend="opt-services.nginx.enable">enable</link> = true;
  <link linkend="opt-services.nginx.virtualHosts">virtualHosts</link> = {
    "foo.example.com" = {
      <link linkend="opt-services.nginx.virtualHosts._name_.forceSSL">forceSSL</link> = true;
      <link linkend="opt-services.nginx.virtualHosts._name_.enableACME">enableACME</link> = true;
      # All serverAliases will be added as <link linkend="opt-security.acme.certs._name_.extraDomainNames">extra domain names</link> on the certificate.
      <link linkend="opt-services.nginx.virtualHosts._name_.serverAliases">serverAliases</link> = [ "bar.example.com" ];
      locations."/" = {
        <link linkend="opt-services.nginx.virtualHosts._name_.locations._name_.root">root</link> = "/var/www";
      };
    };

    # We can also add a different vhost and reuse the same certificate
    # but we have to append extraDomainNames manually.
    <link linkend="opt-security.acme.certs._name_.extraDomainNames">security.acme.certs."foo.example.com".extraDomainNames</link> = [ "baz.example.com" ];
    "baz.example.com" = {
      <link linkend="opt-services.nginx.virtualHosts._name_.forceSSL">forceSSL</link> = true;
      <link linkend="opt-services.nginx.virtualHosts._name_.useACMEHost">useACMEHost</link> = "foo.example.com";
      locations."/" = {
        <link linkend="opt-services.nginx.virtualHosts._name_.locations._name_.root">root</link> = "/var/www";
      };
    };
  };
}
</programlisting>
 </section>
 <section xml:id="module-security-acme-httpd">
  <title>Using ACME certificates in Apache/httpd</title>

  <para>
   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 appropriate.
  </para>
 </section>
 <section xml:id="module-security-acme-configuring">
  <title>Manual configuration of HTTP-01 validation</title>

  <para>
   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 HTTPS.
  </para>

<programlisting>
<xref linkend="opt-security.acme.acceptTerms" /> = true;
<xref linkend="opt-security.acme.email" /> = "admin+acme@example.com";
services.nginx = {
  <link linkend="opt-services.nginx.enable">enable</link> = true;
  <link linkend="opt-services.nginx.virtualHosts">virtualHosts</link> = {
    "acmechallenge.example.com" = {
      # Catchall vhost, will redirect users to HTTPS for all vhosts
      <link linkend="opt-services.nginx.virtualHosts._name_.serverAliases">serverAliases</link> = [ "*.example.com" ];
      # /var/lib/acme/.challenges must be writable by the ACME user
      # and readable by the Nginx user.
      # By default, this is the case.
      locations."/.well-known/acme-challenge" = {
        <link linkend="opt-services.nginx.virtualHosts._name_.locations._name_.root">root</link> = "/var/lib/acme/.challenges";
      };
      locations."/" = {
        <link linkend="opt-services.nginx.virtualHosts._name_.locations._name_.return">return</link> = "301 https://$host$request_uri";
      };
    };
  };
}
# Alternative config for Apache
services.httpd = {
  <link linkend="opt-services.httpd.enable">enable = true;</link>
  <link linkend="opt-services.httpd.virtualHosts">virtualHosts</link> = {
    "acmechallenge.example.com" = {
      # Catchall vhost, will redirect users to HTTPS for all vhosts
      <link linkend="opt-services.httpd.virtualHosts._name_.serverAliases">serverAliases</link> = [ "*.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.
      <link linkend="opt-services.httpd.virtualHosts._name_.documentRoot">documentRoot</link> = "/var/lib/acme/.challenges";
      <link linkend="opt-services.httpd.virtualHosts._name_.extraConfig">extraConfig</link> = ''
        RewriteEngine On
        RewriteCond %{HTTPS} off
        RewriteCond %{REQUEST_URI} !^/\.well-known/acme-challenge [NC]
        RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301]
      '';
    };
  };
}
</programlisting>

  <para>
   Now you need to configure ACME to generate a certificate.
  </para>

<programlisting>
<xref linkend="opt-security.acme.certs"/>."foo.example.com" = {
  <link linkend="opt-security.acme.certs._name_.webroot">webroot</link> = "/var/lib/acme/.challenges";
  <link linkend="opt-security.acme.certs._name_.email">email</link> = "foo@example.com";
  # Since we have a wildcard vhost to handle port 80,
  # we can generate certs for anything!
  # Just make sure your DNS resolves them.
  <link linkend="opt-security.acme.certs._name_.extraDomainNames">extraDomainNames</link> = [ "mail.example.com" ];
};
</programlisting>

  <para>
   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>.
  </para>

  <para>
   Refer to <xref linkend="ch-options" /> for all available configuration
   options for the <link linkend="opt-security.acme.certs">security.acme</link>
   module.
  </para>
 </section>
 <section xml:id="module-security-acme-config-dns">
  <title>Configuring ACME for DNS validation</title>

  <para>
   This is useful if you want to generate a wildcard certificate, since
   ACME servers will only hand out wildcard certs over DNS validation.
   There 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 example using bind.
  </para>

<programlisting>
services.bind = {
  <link linkend="opt-services.bind.enable">enable</link> = true;
  <link linkend="opt-services.bind.extraConfig">extraConfig</link> = ''
    include "/var/lib/secrets/dnskeys.conf";
  '';
  <link linkend="opt-services.bind.zones">zones</link> = [
    rec {
      name = "example.com";
      file = "/var/db/bind/${name}";
      master = true;
      extraConfig = "allow-update { key rfc2136key.example.com.; };";
    }
  ];
}

# Now we can configure ACME
<xref linkend="opt-security.acme.acceptTerms" /> = true;
<xref linkend="opt-security.acme.email" /> = "admin+acme@example.com";
<xref linkend="opt-security.acme.certs" />."example.com" = {
  <link linkend="opt-security.acme.certs._name_.domain">domain</link> = "*.example.com";
  <link linkend="opt-security.acme.certs._name_.dnsProvider">dnsProvider</link> = "rfc2136";
  <link linkend="opt-security.acme.certs._name_.credentialsFile">credentialsFile</link> = "/var/lib/secrets/certs.secret";
  # We don't need to wait for propagation since this is a local DNS server
  <link linkend="opt-security.acme.certs._name_.dnsPropagationCheck">dnsPropagationCheck</link> = false;
};
</programlisting>

  <para>
   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 these commands:
  </para>

<programlisting>
mkdir -p /var/lib/secrets
tsig-keygen rfc2136key.example.com &gt; /var/lib/secrets/dnskeys.conf
chown named:root /var/lib/secrets/dnskeys.conf
chmod 400 /var/lib/secrets/dnskeys.conf

# Copy the secret value from the dnskeys.conf, and put it in
# RFC2136_TSIG_SECRET below

cat &gt; /var/lib/secrets/certs.secret &lt;&lt; EOF
RFC2136_NAMESERVER='127.0.0.1:53'
RFC2136_TSIG_ALGORITHM='hmac-sha256.'
RFC2136_TSIG_KEY='rfc2136key.example.com'
RFC2136_TSIG_SECRET='your secret key'
EOF
chmod 400 /var/lib/secrets/certs.secret
</programlisting>

  <para>
   Now you're all set to generate certs! You should monitor the first invokation
   by running <literal>systemctl start acme-example.com.service &amp;
   journalctl -fu acme-example.com.service</literal> and watching its log output.
  </para>
 </section>
 <section xml:id="module-security-acme-regenerate">
  <title>Regenerating certificates</title>

  <para>
   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 acme-example.com.service</literal>
   will remove all certificate files for the given domain, allowing you to then
   <literal>systemctl start acme-example.com.service</literal> to generate fresh
   ones.
  </para>
 </section>
</chapter>