Log in with MicroStudio for external applications
A login page that can redirect to external sites that use MicroStudio accounts.
https://microstudio.dev/login?redirect=https://example.com/login
Allow "example.com" to access your MicroStudio account?
https://example.com/login?token=YOUR_ACCESS_TOKEN&source=https://microstudio.dev
If it's better not to have the access token in a URL, then there could be a system where the MicroStudio server posts to a given URL. It also wouldn't be hard to create an external application that either has users enter their MicroStudio password or verify their account by replying to a bot on the forum.