SCRAM - support for using Hashed and salted passwords

[davidfrickert]

Hi all,

Reading the documentation of this project it seems to imply that SCRAM needs cleartext passwords in order to work. https://github.com/cyrusimap/cyrus-sasl/blob/master/docsrc/sasl/faqs/plaintextpasswords.rst

However I don't think this is true, as some reference implementations I've seen do store the hash, salt and iterations on the backend instead of the cleartext password.

If storing an hashed password currently is not supported, what could we do to support it?