Single sign-on is a solved problem. You redirect to an identity provider, it tells you who the person is, you mint a session. Every framework has a library for it.

Then you try it on an app that encrypts everything in the browser, and the whole thing falls over.

The claim that breaks SSO

MindMapVault derives your encryption key from your passphrase, in your browser, and never sends it anywhere:

master_key = Argon2id(passphrase, salt)