No good docs on authentication API

[isidorn]

I noticed that our docs are quite limited for the Authentication API
I noticed a sample https://github.com/microsoft/vscode-extension-samples/tree/main/authenticationprovider-sample

But does this require a dedicated Extension Guides page?

[TylerLeonhardt]

Probably... it's a complicated API... we just don't see many extensions that aren't owned by us using these APIs