config/modules/services/nsd-acme/default.nix

{
  config,
  lib,
  pkgs,
  ...
}: let
  cfg = config.mj.services.nsd-acme;
  mkHook = zone: let
    fullZone = "_acme-endpoint.${zone}";
  in
    pkgs.writeShellScript "nsd-acme-hook" ''
      set -euo pipefail
      METHOD=$1
      TYPE=$2
      AUTH=$5
      NOW=$(date +%y%m%d%H%M)
      DIR="/var/lib/nsd/acmezones"

      [ "$TYPE" != "dns-01" ] && { exit 1; }

      write_zone() {
          cat <<EOF
      \$ORIGIN ${fullZone}.
      \$TTL 60
      @      SOA   ${fullZone}. motiejus.jakstys.lt. ($NOW 12h 2h 2w 1h)
      @      TXT   $AUTH
      EOF
      }

      cleanup() {
          nsd-control delzone ${fullZone}
          rm -f "$DIR/${fullZone}.zone"
      }

      mkdir -p "$DIR"

      case "$METHOD" in
          begin)
              nsd-control delzone ${fullZone} || :
              write_zone > "$DIR/${fullZone}.zone"
              nsd-control addzone ${fullZone} acme
              ;;
          done)
              cleanup
              ;;
          failed)
              cleanup
              ;;
      esac
    '';
in {
  options.mj.services.nsd-acme = with lib.types; {
    enable = lib.mkEnableOption "enable acme certs via nsd";

    zones = lib.mkOption {
      default = {};
      type = attrsOf (submodule (
        {name, ...}: {
          options = {
            accountKey = lib.mkOption {type = path;};
            days = lib.mkOption {
              type = int;
              default = 30;
            };
            staging = lib.mkOption {
              type = bool;
              default = false;
            };

            # Warning: paths here are here to be read from. Changing them will
            # not place the files somewhere else.
            certFile = lib.mkOption {
              type = str;
              default = "/var/lib/nsd-acme/${name}/${name}/cert.pem";
            };
            keyFile = lib.mkOption {
              type = str;
              default = "/var/lib/nsd-acme/${name}/private/${name}/key.pem";
            };
          };
        }
      ));
    };
  };

  # TODO assert services.nsd.enable
  config = lib.mkIf cfg.enable {
    services.nsd.remoteControl.enable = true;
    services.nsd.extraConfig = ''
      pattern:
        name: "acme"
        zonefile: "/var/lib/nsd/acmezones/%s.zone"
    '';

    systemd = {
      tmpfiles.rules = ["d /var/lib/nsd/acmezones 0755 nsd nsd -"];

      services =
        {
          nsd-control-setup = {
            requiredBy = ["nsd.service"];
            before = ["nsd.service"];
            unitConfig.ConditionPathExists = let
              rc = config.services.nsd.remoteControl;
            in [
              "|!${rc.controlKeyFile}"
              "|!${rc.controlCertFile}"
              "|!${rc.serverKeyFile}"
              "|!${rc.serverCertFile}"
            ];
            serviceConfig = {
              Type = "oneshot";
              UMask = 0077;
            };
            script = ''
              ${pkgs.nsd}/bin/nsd-control-setup
              chown nsd:nsd /etc/nsd/nsd_{control,server}.{key,pem}
            '';
            path = [pkgs.openssl];
          };
        }
        // lib.mapAttrs'
        (
          zone: cfg:
            lib.nameValuePair "nsd-acme-${zone}" {
              description = "dns-01 acme update for ${zone}";
              path = [pkgs.openssh pkgs.nsd];
              preStart = ''
                mkdir -p "$STATE_DIRECTORY/private"
                ln -sf "$CREDENTIALS_DIRECTORY/letsencrypt-account-key" \
                  "$STATE_DIRECTORY/private/key.pem"
              '';
              serviceConfig = {
                ExecStart = let
                  hook = mkHook zone;
                  days = builtins.toString cfg.days;
                in "${pkgs.uacme}/bin/uacme -c \${STATE_DIRECTORY} --verbose --days ${days} --hook ${hook} ${lib.optionalString cfg.staging "--staging"} issue ${zone}";

                UMask = "0022";
                User = "nsd";
                Group = "nsd";
                StateDirectory = "nsd-acme/${zone}";
                LoadCredential = ["letsencrypt-account-key:${cfg.accountKey}"];
                ReadWritePaths = ["/var/lib/nsd/acmezones"];
                SuccessExitStatus = [0 1];

                # from nixos/modules/security/acme/default.nix
                ProtectSystem = "strict";
                PrivateTmp = true;
                CapabilityBoundingSet = [""];
                DevicePolicy = "closed";
                LockPersonality = true;
                MemoryDenyWriteExecute = true;
                NoNewPrivileges = true;
                PrivateDevices = true;
                ProtectClock = true;
                ProtectHome = true;
                ProtectHostname = true;
                ProtectControlGroups = true;
                ProtectKernelLogs = true;
                ProtectKernelModules = true;
                ProtectKernelTunables = true;
                ProtectProc = "invisible";
                ProcSubset = "pid";
                RemoveIPC = true;
                # "cannot get devices"
                #RestrictAddressFamilies = [
                #  "AF_INET"
                #  "AF_INET6"
                #];
                RestrictNamespaces = true;
                RestrictRealtime = true;
                RestrictSUIDSGID = true;
                SystemCallArchitectures = "native";
                SystemCallFilter = [
                  # 1. allow a reasonable set of syscalls
                  "@system-service @resources"
                  # 2. and deny unreasonable ones
                  "~@privileged"
                  # 3. then allow the required subset within denied groups
                  "@chown"
                ];
              };
            }
        )
        cfg.zones;

      timers =
        lib.mapAttrs'
        (
          zone: _:
            lib.nameValuePair "nsd-acme-${zone}" {
              description = "nsd-acme for zone ${zone}";
              wantedBy = ["timers.target"];
              timerConfig = {
                OnCalendar = "*-*-* 01:30";
              };
              after = ["network-online.target"];
            }
        )
        cfg.zones;
    };

    mj.base.unitstatus.units =
      lib.mkIf config.mj.base.unitstatus.enable
      (
        ["nsd-control-setup"]
        ++ map (z: "nsd-acme-${z}")
        (lib.attrNames cfg.zones)
      );
  };
}