I skimmed over the previous articles in this blog and they don't seem to mention the one use case JWTs were made for: having a separate authentication server from the application server. Most developers will only need this for integrating into corporations with single sign in or social logins (sign in with Facebook/google/apple...). There you won't write the authentication server but integrate with them. Session Ids are dead simple to get right securely. Just use them.
Maybe missed something.
Private key redis key
public static string PrivateKey(string kid) => $"{Root}:jwks:private:{kid}"; // full private material (short life) - 90 days is a very long time to keep keys, I'd expect rotation maybe between 10 minutes and a day? I don't see any justification for this in the article.
- There's no need to keep any private keys except the current signing key and maybe an upcoming key. Old keys should be deleted on rotation, not just left to eventually expire.
- https://github.com/aaroncpina/Aaron.Pina.Blog.Article.08/blob/776e3b365d177ed3b779242181f0045cd6387b3f/Aaron.Pina.Blog.Article.08.Server/Program.cs#L70-L77 - You're not allowed to get a new token if you have a a token already? That's unworkable - what if you want to log in on a new device? Or what if the client fails to receive the token request after the server sends it, the classic snag with use-only-once tokens?
- A fun thing about setting an expiry on the keys is that it makes them eligible for eviction with Redis' standard volatile-lru policy. You can configure this, but it would make me nervous.Would have been good if the article example showed a Redis server with TLS and password auth.
You never have the private key, only the ability to ask something to encrypt/sign something
This is a hard tradeoff between availability and compliance. If the cloud service goes down or you have an internet issue, you would lose the ability to sign any new tokens. This is a fairly fundamental aspect of infrastructure so it's worth considering if you absolutely must put it across the wire.
It crosses from everyone has the keys like in this example, to centralising a signing service using just software, or using something like KMS or CloudHSM, or YubiHSM, or going big and getting a HA Luna (or similar) HSM setup.