Woke up early today and figured I'll tackle this for you. I got it working locally and will provide a PR against the original extension and provide instructions on how to use my version somewhere the next couple of hours.
Edit: pr made (see jslirola/flarum-ext-login2seeplus18)
To use my version while the author readies up the update (if ever):
composer config repositories.login2seeplus vcs https://github.com/luceos/flarum-ext-login2seeplus
composer require jslirola/flarum-ext-login2seeplus:"dev-master"