$client_id = 'XXXXXXXX'; // ID приложения
$client_secret = 'xxxxxxxxxxxxxxxxxxxxxxxxx'; // Защищённый ключ
$redirect_uri = 'https://site.ru/social_login_callback/vk.php'; // куда ответ
$url = 'https://oauth.vk.com/authorize';
$params = array(
'client_id' => $client_id,
'scope' => 'email',
'redirect_uri' => $redirect_uri,
'response_type' => 'code'
);
header('Location: '. $url . '?' . urldecode(http_build_query($params)) ); exit();