SSO Without Giving the Server Your Keys
You redirect to an identity provider, it tells you who the person is, you mint a session. Then you try it on an app that encrypts everything in the browser, and the whole thing falls over.
Useful takeaways from this story.
You redirect to an identity provider, it tells you who the person is, you mint a session.
Both are telling the truth, and neither one helps, because an OIDC token is an assertion about identity — it is not, and cannot be, the key that decrypts Alice's data.
Then you try it on an app that encrypts everything in the browser, and the whole thing falls over.
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The useful part
You redirect to an identity provider, it tells you who the person is, you mint a session. Then you try it on an app that encrypts everything in the browser, and the whole thing falls over. The server stores ciphertext and a hash of auth_token, and that is the entire extent of what it knows.
How it works
- Both are telling the truth, and neither one helps, because an OIDC token is an assertion about identity — it is not, and cannot be, the key that decrypts Alice's data.
What to take from it
Something a device holds — a passkey, or a key in browser storage.
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