dendritic/modules/features/mtls/default.nix

{ self, inputs, lib, ... }:
let
  # Options that will be in common between the nixos module and the home-manager module.
  mkOpts = config: let cfg = config.mtls; in {
    enable = lib.mkEnableOption "Enable mTLS";
    subject = lib.mkOption {
      description = "The Common Name, DNS Name, or IP address that will be set as the Subject Common Name for the certificate. If no Subject Alternative Names (SANs) are configured (via the --san flag) then the subject will be set as the only SAN.";
      type = lib.types.str;
    };
    certDir = lib.mkOption {
      description = "String path to the directory where the certs will be stored";
      type = lib.types.str;
    };
    caFile = lib.mkOption {
      description = "String path for the root CA file";
      type = lib.types.str;
      default = "${cfg.certDir}/root_ca.crt";
    };
    keyFile = lib.mkOption {
      description = "String path for the private key";
      type = lib.types.str;
      default = "${cfg.certDir}/key.pem";
    };
    certFile = lib.mkOption {
      description = "String path for the public cert";
      type = lib.types.str;
      default = "${cfg.certDir}/cert.pem";
    };
    bundleFile = lib.mkOption {
      description = "String path for the mTLS key bundle";
      type = lib.types.str;
      default = "${cfg.certDir}/mtls.pem";
    };
    san = lib.mkOption {
      description = "List of SAN to give the mTLS cert";
      type = lib.types.listOf lib.types.str;
      default = [ ];
    };
    provisioner = lib.mkOption {
      type = lib.types.str;
      default = "admin";
    };
    lifetime = lib.mkOption {
      type = lib.types.str;
      default = "24h";
    };
    renew = {
      enable = lib.mkOption {
        description = "Enable automatic mTLS certificate renewal using a systemd timer.";
        type = lib.types.bool;
        default = cfg.enable;
      };
      onCalendar = lib.mkOption {
        description = "systemd OnCalendar schedule for mTLS certificate renewal checks.";
        type = lib.types.str;
        default = "*:1/15";
      };
      randomizedDelaySec = lib.mkOption {
        description = "Randomized delay added to renewal timer runs to avoid synchronized renewals.";
        type = lib.types.str;
        default = "5m";
      };
      user = lib.mkOption {
        description = "User account to run the mTLS renewal service as.";
        type = lib.types.str;
        default = "root";
      };
      group = lib.mkOption {
        description = "Group to run the mTLS renewal service as. Defaults to the configured renewal user.";
        type = lib.types.nullOr lib.types.str;
        default = "mtls";
      };
      reloadUnits = lib.mkOption {
        description = "systemd units to try-reload-or-restart after a successful certificate renewal.";
        type = lib.types.listOf lib.types.str;
        default = [ ];
      };
      postCommands = lib.mkOption {
        description = "Shell commands to run after a successful certificate renewal.";
        type = lib.types.listOf lib.types.lines;
        default = [ ];
      };
    };
  };
in
{
  flake.modules.nixos.mtls = { config, lib, pkgs, ... }:
    let
      cfg = config.mtls;
      mtlsWrappers = inputs.self.wrappers.mtls;
      mtlsGenerate = mtlsWrappers.generate.apply {
        inherit pkgs;
        inherit (cfg) subject;
        SANs = cfg.san;
        provisioner = "admin";
        provisionerPasswordFile = config.sops.secrets."janus/admin_jwk".path;
      };
      mtlsRenew = mtlsWrappers.renew.apply {
        inherit pkgs;
      };
      mtlsCheck = mtlsWrappers.check.apply {
        inherit pkgs;
      };
    in
    {
      options.mtls = (mkOpts config) // {
        certDir = lib.mkOption {
          description = "String path to where the mtls certs will be stored.";
          type = lib.types.str;
          default = "/etc/step-ca/certs";
        };
        bootstrap = {
          enable = lib.mkOption {
            description = "Enable initial mTLS issuance when cert material is missing or invalid.";
            type = lib.types.bool;
            default = false;
          };
          wantedBy = lib.mkOption {
            description = "systemd targets that should pull in mtls-bootstrap.service.";
            type = with lib.types; listOf str;
            default = [ "multi-user.target" ];
          };
          after = lib.mkOption {
            description = "systemd units/targets that mtls-bootstrap.service should run after.";
            type = with lib.types; listOf str;
            default = [ "network-online.target" ];
          };
          wants = lib.mkOption {
            description = "systemd units/targets that mtls-bootstrap.service should pull in.";
            type = with lib.types; listOf str;
            default = [ "network-online.target" ];
          };
          provisionerPasswordFile = lib.mkOption {
            description = "Optional path passed to mtls-generate as --provisioner-password-file for noninteractive issuance.";
            type = lib.types.nullOr lib.types.str;
            default = null;
          };
        };
        certReaders = lib.mkOption {
          description = "";
          type = lib.types.listOf lib.types.str;
          default = [ ];
        };
      };

      config = lib.mkIf cfg.enable {
        users.groups.certReaders = {
          name = cfg.renew.group;
          members = cfg.certReaders;
        };

        environment.systemPackages = [
          mtlsGenerate.wrapper
          mtlsCheck.wrapper
          mtlsRenew.wrapper
        ];

        systemd = {
          packages = [ mtlsRenew.outputs.systemd-system ];
          # Timer-driven oneshot: only the timer is enabled. NixOS does not
          # honor the unit's [Install] section for systemd.packages, so the
          # wantedBy must be set explicitly here.
          timers.mtls-renew.wantedBy = [ "timers.target" ];
        };
      };
    };
}