migrations/RbacMigration.php
public function init() {
        parent::init();
        $this->authManager = Yii::$app->getAuthManager();
        if (!$this->authManager instanceof DbManager) {
            throw new InvalidConfigException('You should configure "authManager" component to use database before executing this migration.');
        }
    }
public function init() {
        parent::init();
        $this->authManager = Yii::$app->getAuthManager();
        if (!$this->authManager instanceof DbManager) {
            throw new InvalidConfigException('You should configure "authManager" component to use database before executing this migration.');
        }
    }
Initialize migrations.
Calls parent init method, then loads current authManager instance.

@return DbManager
@throws yii\base\InvalidConfigException