Actually I remembered now that the last time I worked with the MySQL protocol (~2014) I had a similar problem: Some of our servers were still running an old version of MySQL so the client had to be backwards compatible. However, this old version of MySQL also used the "old mysql password" authentication which was found to be unsafe/broken at some point. So the MySQL guys deleted the documentation on how the old scheme worked and replaced it with a notice saying that it is insecure. Tough luck if you still had to support/implement it. The same thing has apparently happened here. Not only is the documentation gone, it's actually gone without a trace on the official website.