# Authentik LDAP authentication for NixOS hosts.
#
# Wires SSSD (System Security Services Daemon) to the Authentik LDAP outpost so
# every Linux host authenticates users against the same directory that backs the
# SSO stack. Enabled by default on every NixOS host via baseModules; the EDaaS
# WSL box opts out (services.authentikLdap.enable = false) because it is a
# work-managed Windows-hosted environment.
#
# The Authentik LDAP provider exposes NON-standard object classes/attributes
# (goauthentik.io/ldap/user, goauthentik.io/ldap/group) alongside the POSIX
# attributes (uid, uidNumber, gidNumber, homeDirectory), so the schema mappings
# below are explicit rather than relying on an RFC2307 default.
#
# The bind password is NOT inlined: services.sssd.config renders to the world-
# readable Nix store, so the credential is delivered out-of-band by agenix as an
# sssd.conf drop-in under /etc/sssd/conf.d/ (SSSD merges conf.d/*.conf after the
# main file). See secrets/README.md.
{
  config,
  lib,
  ...
}:
let
  cfg = config.services.authentikLdap;

  # Directory coordinates for the Authentik LDAP provider.
  ldapUri = "ldaps://ldap.lyrapup.pet:636";
  searchBase = "dc=ldap,dc=goauthentik,dc=io";
  bindDn = "cn=sssd-bind,ou=users,dc=ldap,dc=goauthentik,dc=io";
in
{
  options.services.authentikLdap.enable =
    lib.mkEnableOption "SSSD authentication against the Authentik LDAP outpost"
    // {
      default = true;
    };

  config = lib.mkIf cfg.enable {
    services.sssd = {
      enable = true;

      # Non-secret sssd.conf. The bind password is injected separately via the
      # agenix conf.d drop-in (ldap_default_authtok lives there, not here) to
      # keep it out of the Nix store.
      config = ''
        [sssd]
        config_file_version = 2
        services = nss, pam
        domains = default

        [nss]
        # Do not walk the whole directory for `getent passwd` etc.
        filter_users = root
        filter_groups = root

        [pam]

        [domain/default]
        # --- Providers --------------------------------------------------------
        id_provider = ldap
        auth_provider = ldap
        chpass_provider = none
        access_provider = permit

        # --- Connection -------------------------------------------------------
        ldap_uri = ${ldapUri}
        ldap_search_base = ${searchBase}
        ldap_default_bind_dn = ${bindDn}
        ldap_default_authtok_type = password
        # ldap_default_authtok is supplied by the agenix drop-in in conf.d.

        # --- TLS (LDAPS on 636; no StartTLS) ---------------------------------
        ldap_id_use_start_tls = false
        ldap_tls_reqcert = demand

        # --- Schema: Authentik LDAP provider ---------------------------------
        # Authentik returns DN-valued group membership (member/memberOf), so
        # rfc2307bis (not rfc2307) is the correct base schema.
        ldap_schema = rfc2307bis

        # Users: goauthentik.io/ldap/user, keyed by uid; POSIX attrs are
        # standard names (uidNumber/gidNumber/homeDirectory).
        ldap_user_object_class = goauthentik.io/ldap/user
        ldap_user_name = uid
        ldap_user_uid_number = uidNumber
        ldap_user_gid_number = gidNumber
        ldap_user_home_directory = homeDirectory
        ldap_user_gecos = displayName
        ldap_user_shell = loginShell

        # Groups: goauthentik.io/ldap/group, keyed by cn.
        ldap_group_object_class = goauthentik.io/ldap/group
        ldap_group_name = cn
        ldap_group_gid_number = gidNumber
        ldap_group_member = member

        # --- Behaviour --------------------------------------------------------
        cache_credentials = true
        enumerate = false
      '';
    };

    # agenix delivers the bind password as an sssd.conf drop-in. The decrypted
    # plaintext IS a valid conf.d snippet:
    #
    #   [domain/default]
    #   ldap_default_authtok = <the bind password>
    #
    # SSSD requires conf.d files to be root-owned and 0600 or it ignores them.
    age.secrets.ldap-bind = {
      file = ../secrets/ldap-bind.age;
      path = "/etc/sssd/conf.d/01-ldap-authtok.conf";
      owner = "root";
      group = "root";
      mode = "0600";
    };

    # Restart SSSD when the credential drop-in changes. agenix writes secrets in
    # a system activation script that runs before systemd (re)starts services on
    # a `switch`, so the file is present by the time sssd starts; the trigger
    # picks up rotations of the bind password.
    systemd.services.sssd.restartTriggers = [ config.age.secrets.ldap-bind.path ];

    # Create home directories on first login for LDAP users (they have no
    # locally-provisioned home). NixOS wires nss + the SSSD PAM stack when
    # services.sssd.enable is true; mkHomeDir adds pam_mkhomedir to it.
    security.pam.services.login.makeHomeDir = true;
    security.pam.services.sshd.makeHomeDir = true;
  };
}