company-nix/modules/nixos/tailscale-init.nix

{
  config,
  lib,
  pkgs,
  ...
}:
let
  cfg = config.nodeiwest;
  tailscaleOpenbaoCfg = cfg.tailscale.openbao;
in
{
  options.nodeiwest.tailscale.openbao = {
    enable = lib.mkEnableOption "fetching the Tailscale auth key from OpenBao";

    namespace = lib.mkOption {
      type = lib.types.str;
      default = "it";
      description = "OpenBao namespace used when fetching the Tailscale auth key.";
    };

    authPath = lib.mkOption {
      type = lib.types.str;
      default = "auth/approle";
      description = "OpenBao auth mount path used by the AppRole login.";
    };

    secretPath = lib.mkOption {
      type = lib.types.str;
      default = "tailscale";
      description = "OpenBao secret path containing the Tailscale auth key.";
    };

    field = lib.mkOption {
      type = lib.types.str;
      default = "auth_key";
      description = "Field in the OpenBao secret that contains the Tailscale auth key.";
    };

    renderedAuthKeyFile = lib.mkOption {
      type = lib.types.str;
      default = "/run/nodeiwest/tailscale-auth-key";
      description = "Runtime file rendered by OpenBao Agent and consumed by Tailscale autoconnect.";
    };

    approle = {
      roleIdFile = lib.mkOption {
        type = lib.types.str;
        default = "/var/lib/nodeiwest/openbao-approle-role-id";
        description = "Root-only file containing the OpenBao AppRole role_id.";
      };

      secretIdFile = lib.mkOption {
        type = lib.types.str;
        default = "/var/lib/nodeiwest/openbao-approle-secret-id";
        description = "Root-only file containing the OpenBao AppRole secret_id.";
      };
    };
  };

  config = {
    systemd.tmpfiles.rules = [
      "d /var/lib/nodeiwest 0700 root root - -"
      "d /run/nodeiwest 0700 root root - -"
    ];

    services.tailscale = {
      enable = true;
      openFirewall = true;
      extraUpFlags = lib.optionals tailscaleOpenbaoCfg.enable [ "--ssh" ];
      authKeyFile = if tailscaleOpenbaoCfg.enable then tailscaleOpenbaoCfg.renderedAuthKeyFile else null;
    };

    services.vault-agent.instances.tailscale = lib.mkIf tailscaleOpenbaoCfg.enable {
      package = pkgs.openbao;
      settings = {
        vault.address = cfg.openbao.address;
        auto_auth = {
          method = [
            {
              type = "approle";
              mount_path = tailscaleOpenbaoCfg.authPath;
              namespace = tailscaleOpenbaoCfg.namespace;
              config = {
                role_id_file_path = tailscaleOpenbaoCfg.approle.roleIdFile;
                secret_id_file_path = tailscaleOpenbaoCfg.approle.secretIdFile;
                remove_secret_id_file_after_reading = false;
              };
            }
          ];
        };
        template = [
          {
            contents = ''{{- with secret "${tailscaleOpenbaoCfg.secretPath}" -}}{{- if .Data.data -}}{{ index .Data.data "${tailscaleOpenbaoCfg.field}" }}{{- else -}}{{ index .Data "${tailscaleOpenbaoCfg.field}" }}{{- end -}}{{- end -}}'';
            destination = tailscaleOpenbaoCfg.renderedAuthKeyFile;
            perms = "0400";
          }
        ];
      };
    };

    systemd.services.vault-agent-tailscale = lib.mkIf tailscaleOpenbaoCfg.enable {
      wants = [ "network-online.target" ];
      after = [ "network-online.target" ];
      serviceConfig.Environment = [ "BAO_NAMESPACE=${tailscaleOpenbaoCfg.namespace}" ];
    };

    systemd.services.nodeiwest-tailscale-authkey-ready = lib.mkIf tailscaleOpenbaoCfg.enable {
      description = "Wait for the Tailscale auth key rendered by OpenBao Agent";
      after = [ "vault-agent-tailscale.service" ];
      requires = [ "vault-agent-tailscale.service" ];
      before = [ "tailscaled-autoconnect.service" ];
      requiredBy = [ "tailscaled-autoconnect.service" ];
      path = [ pkgs.coreutils ];
      serviceConfig = {
        Type = "oneshot";
      };
      script = ''
        set -euo pipefail

        for _ in $(seq 1 60); do
          if [ -s ${lib.escapeShellArg tailscaleOpenbaoCfg.renderedAuthKeyFile} ]; then
            exit 0
          fi
          sleep 1
        done

        echo "Timed out waiting for rendered Tailscale auth key at ${tailscaleOpenbaoCfg.renderedAuthKeyFile}" >&2
        exit 1
      '';
    };

    systemd.services.tailscaled-autoconnect = lib.mkIf tailscaleOpenbaoCfg.enable {
      after = [
        "vault-agent-tailscale.service"
        "nodeiwest-tailscale-authkey-ready.service"
      ];
      requires = [
        "vault-agent-tailscale.service"
        "nodeiwest-tailscale-authkey-ready.service"
      ];
      serviceConfig.ExecStartPre = [
        "${lib.getExe' pkgs.coreutils "test"} -s ${tailscaleOpenbaoCfg.renderedAuthKeyFile}"
      ];
    };

    assertions = [
      {
        assertion =
          (!tailscaleOpenbaoCfg.enable)
          || (
            tailscaleOpenbaoCfg.approle.roleIdFile != ""
            && tailscaleOpenbaoCfg.approle.secretIdFile != ""
          );
        message = "AppRole roleIdFile and secretIdFile must be set when OpenBao-backed Tailscale enrollment is enabled.";
      }
    ];
  };
}