Was not able to get the SharePoint connected system to work out of the box with client authentication. I think this is due to a change on the SharePoint online side and I had to make some config changes based on this thread:
SharePoint Online authorization issue 'Token type is not allowed' - SharePoint Stack Exchange
Get started with the SharePoint Online Management Shell | Microsoft Docs
Just FYI for anyone running into 401 errors.
Maybe Appian can update the connected system and documentation to use an Azure Enterprise App instead of the old school SharePoint apps.
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Thanks for reporting this, Jake! Just to clarify, are you saying that you had to make some config changes in SharePoint? More specifically, to set DisableCustomAppAuthentication to false?
Yes.