/**
  * @inheritdoc
  */
 public function rules()
 {
     return [['role', 'in', 'range' => Rbac::getRolesNames()]];
 }
<?php

use arogachev\rbac\components\Rbac;
use yii\helpers\Html;
use yii\widgets\ActiveForm;
/* @var $this yii\web\View */
/* @var $model arogachev\rbac\models\AssignRoleToUserForm */
/* @var $form yii\widgets\ActiveForm */
?>

<?php 
$form = ActiveForm::begin();
?>

<?php 
echo $form->field($model, 'role')->dropDownList(Rbac::getRolesMap(), ['prompt' => Yii::t('rbac', 'Without role')]);
?>

<div class="form-group">
    <?php 
echo Html::submitButton(Yii::t('rbac', 'Assign'), ['class' => 'btn btn-primary']);
?>
</div>

<?php 
ActiveForm::end();
?>