Addresses #8579
I might be getting the hang of **_find and replace_** now. 😝
This doesn't touch a couple that ref 2.2.0. I'll tidy those up on https://github.com/aspnet/Docs/issues/8518 after 2.2 RTM.
* initial prose, samples still todo
* add sample and docs on Windows Auth
* add sample download link
* fix some code samples
* fix xref
* clarify sample comment when it's embedded in the document
* pr feedback
* add section on buffer management
* feedback
* some feedback
* update index/toc
* Update authn-and-authz.md