There might be some confusion here, as there is no refusal at all.

As stated in the blog post, we (Prosody) have been accepting (only) serverAuth certificates for a long time. However this is technically in violation of the relevant RFCs, and not the default behaviour of TLS libraries, so it's far from natural for software to be implementing this.

There was only one implementation discovered so far which was not accepting certificates unless they included the clientAuth purpose, and that was already updated 6+ months ago.

This blog post is intended to alert our users, and the broader XMPP community, about the issue that many were unaware of, and particularly to nudge server operators to upgrade their software if necessary, to avoid any federation issues on the network.