This is simple auth extension with vk.com OAuth2.0.
When register it translitirate any cyrillic names to latin, and set user avatar.
I used flarum/auth-facebook as template 🙂
composer require nikovonlas/flarum-ext-auth-vk
Don't forget to activate the extension in the admin panel of your Flarum, and use the Settings dialog to configure the extension!