This is what is needed to be able to implement the `tls-unique` variant
of channel binding. For documentation, read:
RFC5056: On the Use of Channel Bindings to Secure Channels:
https://tools.ietf.org/html/rfc5056
RFC5929: Channel Bindings for TLS: https://tools.ietf.org/html/rfc5929
https://www.iana.org/assignments/channel-binding-types/channel-binding-types.xhtml
RFC5802, Section 6: Salted Challenge Response Authentication Mechanism
(SCRAM) SASL and GSS-API Mechanisms, Channel Binding:
https://tools.ietf.org/html/rfc5802#section-6
As described in the commit message: