SASL / GSSAPI support

[NiQ1]

As requested in the clean slate notification, I'm opening a new issue.

Feature request: Implement SASL / GSSAPI binding. There are a couple of TODOs in the code regarding this.

[Gavin152]

There has been a PR with a seemingly working implementation for SASL auth in #826. I don't know what happened to the thread after the v3 relaese, though.

[jsumners]

Anyone is welcome to carry that work forward. Please make sure to keep the history of existing work (if it still applies) so that the original author gets credit -- https://gist.github.com/jsumners/461ef7a64545108635cc437fde112721

[Gavin152]

Ok, thanks. I may look into it in the near future. And yes, credit shall of course be given!