Hey, swinging back around on this. Now that oauth is being used extensively by the 
Dashboard in /settings/admin/connected-accounts I’m wondering if we’ll finally be able to get Kanboard and DokuWiki authenticating.
Hoping to update current status on this… thanks for spending so much time sorting through it!
Current Documentation to set up Oauth 2 in Nextcloud
OCS Api issue fixed
Redirection error addressed
Actively developed oauth plugin for DokuWiki
Security Warning!
Nextcloud OAuth2 implementation currently does not support scoped access. This means that every token has full access to the complete account including read and write permission to the stored files. It is essential to store the OAuth2 tokens in a safe way!
Without scopes and restrictable access it is not recommended to use a Nextcloud instance as a user authentication service.