> I wonder why we can't just have an https-based known-file challenge that works exactly like the http one, but over https, and just accepts whatever cert you t

> I wonder why we can't just have an https-based known-file challenge that works exactly like the http one, but over https, and just accepts whatever cert you throw at it initially. This method was called HTTPS-01 and was initially discussed at the IETF ACME WG. My recollection is that it was rejected for a reason similar to why TLS-SNI-01 has just been disabled: many hosting providers' practices would designate one customer as the default HTTPS virtual host for all incoming HTTPS requests. Therefore, that customer would be in a position to get a certificate for any other customer on that infrastructure. This problem was easier to notice for HTTPS-01 than the corresponding problem with TLS-SNI-01 (which is that you can upload invalid certificates for names that aren't hosted on the infrastructure at all, and thereby get some shared hosting environments to believe that they're third-party certificates for your own sites that you've imported from elsewhere, while they're actually ACME challenge certificates for a different customer on the same infrastructure).