<?php
namespace appbootstraps;
use yiibaseBootstrapInterface;

class AppBootstrap implements BootstrapInterface{

   public function bootstrap($app){
      $app->user->on(yiiwebUser::EVENT_BEFORE_LOGIN,['appmodelsuserUser', 'beforeLogin']);
      $app->user->on(yiiwebUser::EVENT_AFTER_LOGIN,['appmodelsuserUser', 'afterLogin']);
      $app->user->on(yiiwebUser::EVENT_BEFORE_LOGOUT,['appmodelsuserUser', 'beforeLogout']);
   }
}

$config = [
    'id' => 'basic',
    'name' => 'x',
    'basePath' => dirname(__DIR__),
    'bootstrap' => [
        'log',
        'appbootstrapsAppBootstrap',
    ],
.....etc

public function afterLogin($identity, $cookieBased, $duration){
        parent::afterLogin($identity, $cookieBased, $duration);
        // your code here, such set session
   }