nixos/acme: replace simp-le with lego client

Lego allows users to use the DNS-01 challenge to validate their
certificates. It is mostly backwards compatible, with a few
caveats.

 - extraDomains can no longer have different webroots to the
   main webroot for the cert.
 - An email address is now mandatory for account creation

The following other changes were required:
 - Deprecate security.acme.certs.<name>.plugins, as this was
   specific to simp-le
 - Rename security.acme.validMin to validMinDays, to avoid
   confusion and errors. Lego requires the TTL to be specified in
   days
 - Add options to cover DNS challenge (dnsProvider,
   credentialsFile, dnsPropagationCheck)
 - A shared state directory is now used (/var/lib/acme/.lego)
   to avoid account creation rate limits and share credentials
   between certs

nixos/modules/security/acme.nix

@@ -1,7 +1,5 @@
 { config, lib, pkgs, ... }:
-
 with lib;
-
 let
 
   cfg = config.security.acme;
@@ -76,20 +74,6 @@ let
         '';
       };
 
-      plugins = mkOption {
-        type = types.listOf (types.enum [
-          "cert.der" "cert.pem" "chain.pem" "external.sh"
-          "fullchain.pem" "full.pem" "key.der" "key.pem" "account_key.json" "account_reg.json"
-        ]);
-        default = [ "fullchain.pem" "full.pem" "key.pem" "account_key.json" "account_reg.json" ];
-        description = ''
-          Plugins to enable. With default settings simp_le will
-          store public certificate bundle in <filename>fullchain.pem</filename>,
-          private key in <filename>key.pem</filename> and those two previous
-          files combined in <filename>full.pem</filename> in its state directory.
-        '';
-      };
-
       directory = mkOption {
         type = types.str;
         readOnly = true;
@@ -111,6 +95,31 @@ let
           own server roots if needed.
         '';
       };
+
+      dnsProvider = mkOption {
+        type = types.nullOr types.str;
+        example = "route53";
+        default = null;
+        description = "DNS Challenge provider";
+      };
+
+      credentialsFile = mkOption {
+        type = types.str;
+        description = ''
+          File containing DNS provider credentials passed as environment variables.
+          See https://go-acme.github.io/lego/dns/ for more information.
+        '';
+        example = "/var/src/secrets/example.org-route53-api-token";
+      };
+
+      dnsPropagationCheck = mkOption {
+        type = types.bool;
+        default = true;
+        description = ''
+          Toggles LEGo DNS propagation check, which is used alongside DNS-01
+          challenge to ensure the DNS entries required are available
+        '';
+      };
     };
   };
 
@@ -130,14 +139,21 @@ in
     (mkRemovedOptionModule [ "security" "acme" "directory"] "ACME Directory is now hardcoded to /var/lib/acme and its permisisons are managed by systemd. See https://github.com/NixOS/nixpkgs/issues/53852 for more info.")
     (mkRemovedOptionModule [ "security" "acme" "preDelay"] "This option has been removed. If you want to make sure that something executes before certificates are provisioned, add a RequiredBy=acme-\${cert}.service to the service you want to execute before the cert renewal")
     (mkRemovedOptionModule [ "security" "acme" "activationDelay"] "This option has been removed. If you want to make sure that something executes before certificates are provisioned, add a RequiredBy=acme-\${cert}.service to the service you want to execute before the cert renewal")
+    (mkChangedOptionModule [ "security" "acme" "validMin"] [ "security" "acme" "validMinDays"] (config: config.security.acme.validMin / (24 * 3600)))
   ];
   options = {
     security.acme = {
 
-      validMin = mkOption {
+      validMinDays = mkOption {
         type = types.int;
-        default = 30 * 24 * 3600;
+        default = 30;
-        description = "Minimum remaining validity before renewal in seconds.";
+        description = "Minimum remaining validity before renewal in days.";
+      };
+
+      email = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        description = "Contact email address for the CA to be able to reach you.";
       };
 
       renewInterval = mkOption {
@@ -173,6 +189,15 @@ in
         '';
       };
 
+      acceptTerms = mkOption {
+        type = types.bool;
+        default = true;
+        description = ''
+          Accept the current Let's Encrypt terms of service.
+          See https://letsencrypt.org/repository/
+        '';
+      };
+
       certs = mkOption {
         default = { };
         type = with types; attrsOf (submodule certOpts);
@@ -204,27 +229,47 @@ in
   config = mkMerge [
     (mkIf (cfg.certs != { }) {
 
+      assertions = let
+        certs = (mapAttrsToList (k: v: v) cfg.certs);
+      in [
+        {
+          assertion = all (certOpts: certOpts.dnsProvider == null || certOpts.webroot == null) certs;
+          message = ''
+            Options `security.acme.certs.<name>.dnsProvider` and
+            `security.acme.certs.<name>.webroot` are mutually exclusive.
+          '';
+        }
+        {
+          assertion = cfg.email != null || all (certOpts: certOpts.email != null) certs;
+          message = ''
+            You must define `security.acme.certs.<name>.email` or
+            `security.acme.email` to register with the CA.
+          '';
+        }
+      ];
+
       systemd.services = let
           services = concatLists servicesLists;
           servicesLists = mapAttrsToList certToServices cfg.certs;
           certToServices = cert: data:
               let
+                # StateDirectory must be relative, and will be created under /var/lib by systemd
                 lpath = "acme/${cert}";
+                apath = "/var/lib/${lpath}";
+                spath = "/var/lib/acme/.lego";
                 rights = if data.allowKeysForGroup then "750" else "700";
-                cmdline = [ "-v" "-d" data.domain "--default_root" data.webroot "--valid_min" cfg.validMin ]
+                globalOpts = [ "-d" data.domain "--email" data.email "--path" "." ]
-                          ++ optionals (data.email != null) [ "--email" data.email ]
+                          ++ optionals (cfg.acceptTerms) [ "--accept-tos" ]
-                          ++ concatMap (p: [ "-f" p ]) data.plugins
+                          ++ optionals (data.dnsProvider != null && !cfg.dnsPropagationCheck) [ "--dns.disable-cp" ]
-                          ++ concatLists (mapAttrsToList (name: root: [ "-d" (if root == null then name else "${name}:${root}")]) data.extraDomains)
+                          ++ concatLists (mapAttrsToList (name: root: [ "-d" name ]) data.extraDomains)
+                          ++ (if data.dnsProvider != null then [ "--dns" data.dnsProvider ] else [ "--http" "--http.webroot" data.webroot ])
                           ++ optionals (cfg.server != null || data.server != null) ["--server" (if data.server == null then cfg.server else data.server)];
+                runOpts = escapeShellArgs (globalOpts ++ [ "run" ]);
+                renewOpts = escapeShellArgs (globalOpts ++ [ "renew" "--days" (toString cfg.validMinDays) ]);
                 acmeService = {
                   description = "Renew ACME Certificate for ${cert}";
                   after = [ "network.target" "network-online.target" ];
                   wants = [ "network-online.target" ];
-                  # simp_le uses requests, which uses certifi under the hood,
-                  # which doesn't respect the system trust store.
-                  # At least in the acme test, we provision a fake CA, impersonating the LE endpoint.
-                  # REQUESTS_CA_BUNDLE is a way to teach python requests to use something else
-                  environment.REQUESTS_CA_BUNDLE = "/etc/ssl/certs/ca-certificates.crt";
                   serviceConfig = {
                     Type = "oneshot";
                     # With RemainAfterExit the service is considered active even
@@ -233,18 +278,36 @@ in
                     # the permissions of the StateDirectory get adjusted
                     # according to the specified group
                     RemainAfterExit = true;
-                    SuccessExitStatus = [ "0" "1" ];
                     User = data.user;
                     Group = data.group;
                     PrivateTmp = true;
-                    StateDirectory = lpath;
+                    StateDirectory = "acme/.lego ${lpath}";
                     StateDirectoryMode = rights;
-                    WorkingDirectory = "/var/lib/${lpath}";
+                    WorkingDirectory = spath;
-                    ExecStart = "${pkgs.simp_le}/bin/simp_le ${escapeShellArgs cmdline}";
+                    # Only try loading the credentialsFile if the dns challenge is enabled
+                    EnvironmentFile = if data.dnsProvider != null then data.credentialsFile else null;
+                    ExecStart = pkgs.writeScript "acme-start" ''
+                      #!${pkgs.runtimeShell} -e
+                      ${pkgs.lego}/bin/lego ${renewOpts} || ${pkgs.lego}/bin/lego ${runOpts}
+                    '';
                     ExecStartPost =
                       let
                         script = pkgs.writeScript "acme-post-start" ''
                           #!${pkgs.runtimeShell} -e
+                          cd ${apath}
+
+                          # Test that existing cert is older than new cert
+                          KEY=${spath}/certificates/*${data.domain}.key
+                          if [ -e $KEY -a $KEY -nt key.pem ]; then
+                            cp -p ${spath}/certificates/*${data.domain}.key key.pem
+                            cp -p ${spath}/certificates/*${data.domain}.crt cert.pem
+                            cp -p ${spath}/certificates/*${data.domain}.issuer.crt chain.pem
+                            cat cert.pem chain.pem > fullchain.pem
+                            cat key.pem cert.pem chain.pem > full.pem
+                            chmod ${rights} *.pem
+                            chown '${data.user}:${data.group}' *.pem
+                          fi
+
                           ${data.postRun}
                         '';
                       in
@@ -276,17 +339,17 @@ in
                         -out $workdir/server.crt
 
                       # Copy key to destination
-                      cp $workdir/server.key /var/lib/${lpath}/key.pem
+                      cp $workdir/server.key ${apath}/key.pem
 
                       # Create fullchain.pem (same format as "simp_le ... -f fullchain.pem" creates)
-                      cat $workdir/{server.crt,ca.crt} > "/var/lib/${lpath}/fullchain.pem"
+                      cat $workdir/{server.crt,ca.crt} > "${apath}/fullchain.pem"
 
                       # Create full.pem for e.g. lighttpd
-                      cat $workdir/{server.key,server.crt,ca.crt} > "/var/lib/${lpath}/full.pem"
+                      cat $workdir/{server.key,server.crt,ca.crt} > "${apath}/full.pem"
 
                       # Give key acme permissions
-                      chown '${data.user}:${data.group}' "/var/lib/${lpath}/"{key,fullchain,full}.pem
+                      chown '${data.user}:${data.group}' "${apath}/"{key,fullchain,full}.pem
-                      chmod ${rights} "/var/lib/${lpath}/"{key,fullchain,full}.pem
+                      chmod ${rights} "${apath}/"{key,fullchain,full}.pem
                     '';
                   serviceConfig = {
                     Type = "oneshot";
@@ -297,7 +360,7 @@ in
                   };
                   unitConfig = {
                     # Do not create self-signed key when key already exists
-                    ConditionPathExists = "!/var/lib/${lpath}/key.pem";
+                    ConditionPathExists = "!${apath}/key.pem";
                   };
                 };
               in (
@@ -334,7 +397,7 @@ in
   ];
 
   meta = {
-    maintainers = with lib.maintainers; [ abbradar fpletz globin ];
+    maintainers = with lib.maintainers; [ abbradar fpletz globin m1cr0man ];
     doc = ./acme.xml;
   };
 }

nixos/modules/security/acme.xml

@@ -7,7 +7,7 @@
  <para>
   NixOS supports automatic domain validation &amp; certificate retrieval and
   renewal using the ACME protocol. This is currently only implemented by and
-  for Let's Encrypt. The alternative ACME client <literal>simp_le</literal> is
+  for Let's Encrypt. The alternative ACME client <literal>LEGo</literal> is
   used under the hood.
  </para>
  <section xml:id="module-security-acme-prerequisites">