I've used client certificates for a while for my self-hosted stuff, and the UX is pretty terrible.
The moment you have a certificate loaded into your browser, every single tracker will see the availability of client side certificates as a means to do fingerprinting. Either you configure your browser to expose your identity to every website who asks, or you get popups for every other website asking you to pick a certificate.
Web browser could probably fix this, but client certificates are uncommon enough that I doubt they care anymore. Like HTTP basic auth (and its lack of password manager integration), it seems like this feature only remains for compatibility reasons.
Like usual, middleboxes also tend to fuck up client certificate based authentication because they can't effectively MitM those connections (they don't have the key material you're using, and while they can try to fake a website's TLS certificate in intranets, they can't fake your credentials to remote servers).
It's real unfortunate. They're still used, though; some Kubernetes networking tools automatically provision client certs to authenticate API clients within the cluster (as well as protect the traffic from snooping).
I use client certificates since they are required in my line of business and had the impression that they are only presented when asked for by the website, only I explicitly allow it.
Other than the sites that I know require them, I have never been asked to choose a certificate when browsing random websites (windows 11).
Oh, they're not always presented when asked! That'd be one hell of a privacy risk. I think there's a setting for IE/Edge that'll automatically present them for intranet websites, but public websites will prompt you first (unless you dig into the registry and override this behaviour).
Maybe the situation changed, or ad blockers have become better in the mean time, but last time I used them in Firefox, I was bombarded by client certificate requests browsing around the web.
The problem I have with the UX is that the certificate selection screen is a modal dialog that any URL seems to be able to bring up, and I found this abused in the wild. This, combined what made with the countless requests, made me move away from using them.
Another issue I struggled with was that every now and then I'd pick the wrong certificate and I couldn't for the life of me figure out how to correct this without restarting my browser and losing all my work. Switching between accounts for cert based auth was plain impossible.
Lastly there was the entirely unhelpful error state you can end up with when using client certs. Vague HTTPS errors that come down to "oh no something went wrong try reloading I guess" and weird side effect when certificates expired (from browsers sending old certificates to servers accepting expired certificates). The errors occur in the TLS layer, so you end up with authentication errors thst seemingly end up being handled as connection issues.
If you say these issues have been resolved, I should probably give mTLS another go.
FWIW I don’t use FF on the machine where I have the certificates installed, and before I setup network adblockers, had only clienside ones in chrome, and used edge mostly for the sites that needed them, for the past several years.
The UI can be clunky, especially if you set up the certificates to be stored in TPM, since then windows sometimes pops up the dialog in a way that’s easy to miss. Other than that Ive no complaints. Good luck!
The moment you have a certificate loaded into your browser, every single tracker will see the availability of client side certificates as a means to do fingerprinting. Either you configure your browser to expose your identity to every website who asks, or you get popups for every other website asking you to pick a certificate.
Web browser could probably fix this, but client certificates are uncommon enough that I doubt they care anymore. Like HTTP basic auth (and its lack of password manager integration), it seems like this feature only remains for compatibility reasons.
Like usual, middleboxes also tend to fuck up client certificate based authentication because they can't effectively MitM those connections (they don't have the key material you're using, and while they can try to fake a website's TLS certificate in intranets, they can't fake your credentials to remote servers).
It's real unfortunate. They're still used, though; some Kubernetes networking tools automatically provision client certs to authenticate API clients within the cluster (as well as protect the traffic from snooping).