nixpkgs/nixos/modules/programs/shadow.nix

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

{ config, lib, pkgs, ... }:

with lib;

let

  loginDefs =
    ''
      DEFAULT_HOME yes

      SYS_UID_MIN  400
      SYS_UID_MAX  499
      UID_MIN      1000
      UID_MAX      29999

      SYS_GID_MIN  400
      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 = 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.
      '';
      example = "/run/current-system/sw/bin/zsh";
      type = types.path;
    };

  };


  ###### implementation

  config = {

    environment.systemPackages =
      lib.optional config.users.mutableUsers 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 =
      { chsh = { rootOK = true; };
        chfn = { rootOK = true; };
        su = { rootOK = true; forwardXAuth = true; logFailures = true; };
        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.
        useradd = { rootOK = true; };
        usermod = { rootOK = true; };
        userdel = { rootOK = true; };
        groupadd = { rootOK = true; };
        groupmod = { rootOK = true; };
        groupmems = { rootOK = true; };
        groupdel = { rootOK = true; };
        login = { startSession = true; allowNullPassword = true; showMotd = true; updateWtmp = true; };
        chpasswd = { rootOK = true; };
        chgpasswd = { rootOK = true; };
      };

    security.setuidPrograms = [ "su" "chfn" ]
      ++ lib.optionals config.users.mutableUsers
      [ "passwd" "sg" "newgrp"
        "newuidmap" "newgidmap" # new in shadow 4.2.x
      ];

  };

}