Go to the [https://developers.facebook.com/](https://developers.facebook.com/) and create your app.

Click Add product and choose Facebook Login

Before install this extension, you must install yii2-app. In this example, I use yii2-basic template. Guide for installation in here.

Run

composer require --prefer-dist yiisoft/yii2-authclient

or add

"yiisoft/yii2-authclient": "~2.1.0"

to the require section of your composer.json.

Add config authClientCollection to your config components:

return [
    'components' => [
        'authClientCollection' => [
            'class' => 'yii\authclient\Collection',
            'clients' => [
                'facebook' => [
                    'class' => 'yii\authclient\clients\Facebook',
                    'clientId' => 'facebook_client_id',
                    'clientSecret' => 'facebook_client_secret',
                ],
            ],
        ]
    ],
    // ...
];

facebook_client_id is application id and facebook_client_secret is app secret.

1. Add button Login as facebook account to your login view:

Edit site/login.php in views folder, add theses line to content of page login:

<?= yii\authclient\widgets\AuthChoice::widget([
     'baseAuthUrl' => ['site/auth'],
     'popupMode' => false,
]) ?>

Above, we set that auth action in SiteController will handler OAuth2 flow.

Now we create it.

class SiteController extends Controller
{
    public function actions()
    {
        return [
            'auth' => [
                'class' => 'yii\authclient\AuthAction',
                'successCallback' => [$this, 'onAuthSuccess'],
            ],
        ];
    }

    public function onAuthSuccess($client)
    {
        // do many stuff here, save user info to your app database
    }
}

We use yii\authclient\AuthAction for create url and redirect to facebook login page.

Function onAuthSuccess used to get user info, login to your app.

If you enable prettyUrl in your yii2-app, your redirect_uri will be:

http://<base_url>/web/site/auth

And disable pretty url:

http://<base_url>/web/index.php?r=site%2Fauth

Example:

/**
 * @param $client ClientInterface
 */
public function onAuthSuccess($client)
{
    //Get user info
    /** @var array $attributes */
    $attributes = $client->getUserAttributes();
    $email = ArrayHelper::getValue($attributes, 'email'); //email info
    $id = ArrayHelper::getValue($attributes, 'id'); // id facebook user
    $name = ArrayHelper::getValue($attributes, 'name'); // name facebook account

    //Login user
    //For demo, I will login with admin/admin default account
    $admin = User::findByUsername('admin');
    Yii::$app->user->login($admin);
}