I put together a basic proof of concept for using existing #Mastodon installations as SSO for #Matrix, using #Synapse. Here's what the authentication and authorization flow for that looks like!

While Mastodon doesn't support #OpenlD Connect, OIDC is just OpenlD on top of OAuth2.0. If your app allows configuring all URLS for your ldP you can use nearly any OAuth2.0 provider.

Avatars currently aren't supported via this (| added one) but can be! Working on a patch for Synapse!