alt Hacker NewsA public CA checks it one-time, when it's being issued. Most/all mTLS use-cases don't do any checking of the client cert in any capacity. Worse still, some APIs (mainly for finance companies) require things like OV and EV, but of course they couldn't check the Subject DN if they wanted to.
If it's for auth, issue it yourself and don't rely on a third-party like a public CA.
Replies
> A public CA checks it one-time, when it's being issued.
That's the same problem we have with server certs, and the general solution seems to be "shorter cert lifetimes".
> Worse still, some APIs (mainly for finance companies) require things like OV and EV, but of course they couldn't check the Subject DN if they wanted to.
Not an expert there, but isn't the point of EV that the CA verified the "real life entity" that requested the cert? So then it depends on what kind of access model the finance company was specifying for its API. "I don't care who is using my API as long as they are a company" is indeed a very stupid access model, but then I think the problem is deeper than just cert validation.
A federated ecosystem of servers that need to verify each other based on their domain name as the identity is the prime use-case for a public CA to issue domain-verified client certificates. XMPP happens to be this ecosystem.
Rolling out a private PKI for XMPP, with a dedicated Root CA, would be a significant effort, essentially redoing all the hard work of LetsEncrypt, but without the major funding, thus ending up with an insecure solution.
We make use of the public CAs, that have been issuing TLS certificates based on domain validation, for quite a few years now, before the public TLS CAs have been subverted to become public HTTPS-only CAs by Google and the CA/Browser Forum.