nixpkgs/nixos/modules/programs/shadow.nix

# Configuration for the pwdutils suite of tools: passwd, useradd, etc.

{ config, pkgs, ... }:

with pkgs.lib;

let

  loginDefs =
    ''
      DEFAULT_HOME yes

      SYS_UID_MIN  100
      SYS_UID_MAX  499
      UID_MIN      1000
      UID_MAX      29999

      SYS_GID_MIN  100
      SYS_GID_MAX  499
      GID_MIN      1000
      GID_MAX      29999

      TTYGROUP     tty
      TTYPERM      0620

      # Ensure privacy for newly created home directories.
      UMASK        077

      # Uncomment this to allow non-root users to change their account
      #information.  This should be made configurable.
      #CHFN_RESTRICT frwh

    '';

in

{

  ###### interface

  options = {

    users.defaultUserShell = pkgs.lib.mkOption {
      description = ''
        This option defines the default shell assigned to user
        accounts.  This must not be a store path, since the path is
        used outside the store (in particular in /etc/passwd).
        Rather, it should be the path of a symlink that points to the
        actual shell in the Nix store.
      '';
      type = types.uniq types.path;
    };

  };


  ###### implementation

  config = {

    environment.systemPackages = [ pkgs.shadow ];

    environment.etc =
      [ { # /etc/login.defs: global configuration for pwdutils.  You
          # cannot login without it!
          source = pkgs.writeText "login.defs" loginDefs;
          target = "login.defs";
        }

        { # /etc/default/useradd: configuration for useradd.
          source = pkgs.writeText "useradd"
            ''
              GROUP=100
              HOME=/home
              SHELL=${config.users.defaultUserShell}
            '';
          target = "default/useradd";
        }
      ];

    security.pam.services =
      [ { name = "chsh"; rootOK = true; }
        { name = "chfn"; rootOK = true; }
        { name = "su"; rootOK = true; forwardXAuth = true; }
        { name = "passwd"; }
        # Note: useradd, groupadd etc. aren't setuid root, so it
        # doesn't really matter what the PAM config says as long as it
        # lets root in.
        { name = "useradd"; rootOK = true; }
        { name = "usermod"; rootOK = true; }
        { name = "userdel"; rootOK = true; }
        { name = "groupadd"; rootOK = true; }
        { name = "groupmod"; rootOK = true; }
        { name = "groupmems"; rootOK = true; }
        { name = "groupdel"; rootOK = true; }
        { name = "login"; startSession = true; allowNullPassword = true; showMotd = true; updateWtmp = true; }
      ];

    security.setuidPrograms = [ "passwd" "chfn" "su" "newgrp" ];

  };

}