$client_id = 'XXXXXXXXXXXXXXXXXXXXXXX'; // Id приложения
$client_secret = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'; // Пароль приложения
$redirect_uri = 'https://seolik.ru/social_login_callback/yandex.php'; // Callback URI
$url = 'https://oauth.yandex.ru/authorize';
$params = array(
'response_type' => 'code',
'client_id' => $client_id,
'display' => 'popup'
);
header('Location: '. $url . '?' . urldecode(http_build_query($params)) ); exit()