There's loads of non web, non HTTPS TLS use cases, it's just the CAB doesn't care about those (why should it?).
However, eventually, the CABF started imposing restrictions on the public CA operators regarding the issuance of non-HTTPS certificates. Nominally, the CAs are still offering "TLS certificates", but due to the pressure from the CABF, the allowed certificates are getting more and more limited, with the removal of SRVname a few years ago, and the removal of clientAuth that this thread is about.
I can understand the CABF position of "just make your own PKI" to a degree, but in practice that would require a LetsEncrypt level of effort for something that is already perfectly provided by LetsEncrypt, if it wouldn't be for the CABF lobbying.
The restriction is on signing non web certificates with the same root/intermediate as is part of the WebPKI.
There's no rule (that I'm aware of?) that says the CAs can't have different signing roots for whatever use-case that are then trusted by people who need that use case.
[citation needed]
The title of their current (2.2.2) standard is "Baseline Requirements for the Issuance and Management of Publicly‐Trusted TLS Server Certificates":
* https://cabforum.org/working-groups/server/baseline-requirem...
§1.3, "PKI Participants", states:
> The CA/Browser Forum is a voluntary organization of Certification Authorities and suppliers of Internet browser and other relying‐party software applications.
IMHO "other relying-party software applications" can include XMPP servers (also perhaps SMTP, IMAP, FTPS, NNTP, etc).
My citation is the membership of the CAB.
> IMHO "other relying-party software applications" can include XMPP servers (also perhaps SMTP, IMAP, FTPS, NNTP, etc).
This may be your opinion, but what's the representation of XMPP etc. software maintainers at the CAB?
> My citation is the membership of the CAB.
It is a single member of the CAB that is insisting on changing the MAY to a MUST NOT for clientAuth. Why does that single member, Google-Chrome, get to dictate this?
Has Mozilla insisted on changing the meaning of §1.3 to basically remove "other relying‐party software applications"? Apple-Safari? Or any other of the "Certificate Consumers":
* https://cabforum.org/working-groups/server/#certificate-cons...
The membership of CAB collectively agree to the requirements/restrictions they places on themselves, and those requirements (a) state both browser and non-browser use cases, and (b) explicitly allow clientAuth usage as a MAY; see §7.1.2.10.6, §7.1.2.7.10:
* https://cabforum.org/working-groups/server/baseline-requirem...
