@Mastodon want to enhance the onboarding process with single sign-on (SAML) and offer multiple accounts and group management?! Take a look at https://github.com/SURFnet/slurf
We use this solution for a Mastodon instance for Dutch students, researchers and staff from multiple institutions.
They can use their existing edu credentials to register and logon to Mastodon and focus on exploring and getting to know Mastodon and the Fediverse!
https:/social.edu.nl