Added Controller::populate().

app/protected/controllers/SiteController.php

 <?php
 
+use yii\web\Controller;
 use app\models\LoginForm;
-use app\models\User;
 
-class SiteController extends \yii\web\Controller
+class SiteController extends Controller
 {
 	public function actionIndex()
 	{
@@ -13,15 +13,13 @@ class SiteController extends \yii\web\Controller
 	public function actionLogin()
 	{
 		$model = new LoginForm();
-		if (isset($_POST[$model->formName()])) {
-			$model->attributes = $_POST[$model->formName()];
-			if ($model->login()) {
-				Yii::$app->getResponse()->redirect(array('site/index'));
-			}
+		if ($this->populate($_POST, $model) && $model->login()) {
+			Yii::$app->getResponse()->redirect(array('site/index'));
+		} else {
+			echo $this->render('login', array(
+				'model' => $model,
+			));
 		}
-		echo $this->render('login', array(
-			'model' => $model,
-		));
 	}
 
 	public function actionLogout()

app/protected/models/LoginForm.php

@@ -42,7 +42,7 @@ class LoginForm extends Model
 	{
 		if ($this->validate()) {
 			$user = User::findByUsername($this->username);
-			Yii::$app->getUser()->login($user);
+			Yii::$app->getUser()->login($user, $this->rememberMe ? 3600*24*30 : 0);
 			return true;
 		} else {
 			return false;

framework/base/Controller.php

@@ -303,6 +303,34 @@ class Controller extends Component
 	}
 
 	/**
+	 * Populates one or multiple models from the given data array.
+	 * @param array $data the data array. This is usually `$_POST` or `$_GET`, but can also be any valid array.
+	 * @param Model $model the model to be populated. If there are more than one model to be populated,
+	 * you may supply them as additional parameters.
+	 * @return boolean whether at least one model is successfully populated with the data.
+	 */
+	public function populate($data, $model)
+	{
+		$success = false;
+		if (!empty($data) && is_array($data)) {
+			$models = func_get_args();
+			array_shift($models);
+			foreach ($models as $model) {
+				/** @var Model $model */
+				$scope = $model->formName();
+				if ($scope == '') {
+					$model->attributes = $data;
+					$success = true;
+				} elseif (isset($data[$scope])) {
+					$model->attributes = $data[$scope];
+					$success = true;
+				}
+			}
+		}
+		return $success;
+	}
+
+	/**
 	 * Renders a view and applies layout if available.
 	 *
 	 * The view to be rendered can be specified in one of the following formats: