Doc update needed for "Auth Modes"

[poikilotherm]

As @pdurbin pointed out on IRC today, the section about "Auth Modes" needs an update, as referenced issues have been closed since.

Docs about Auth Modes in v4.11

[pdurbin]

Huh, pull request #6105 had the "closes" syntax but this issue was never closed.

This issue is on my mind after a conversation with @kcondon yesterday about pull request #6192 because it's looking like the OAuth support for Microsoft that's coming is not oriented toward centralized auth like ORCID, GitHub, and Google. So I'm feeling like more of a rewrite is needed.

@poikilotherm any thoughts on this? You opened this issue originally. Should we just close it? I can repeat what I said above over in the pull request for Microsoft OAuth stuff.

[poikilotherm]

I guess we can close this to cleanup.