Flarum Steam Authentication
Allow user to login to Flarum with their Steam account

How To Install
Run below command while you're in Flarum root folder to install the extension:
composer require sijad/flarum-ext-auth-steam
now you need to enable this extension in Flarum admin page and set API key in settings
you can get API keys from https://steamcommunity.com/dev/apikey
P.S. I didn't test this extension myself, thanks to @Kulga and @VIRUXE for helping me