Are you running a Discourse forum and Nextcloud?
Here is a great plugin for those running a Discourse forum that want to use to to authenticate forum users, or a group of users, to their Nextcloud server.
Over the last week I’ve written a small service which can be used to act as an OpenID connect/OAuth provider with discourse as a backend. Note that my primary use case was to authenticate to Nextcloud using Discourse, so it might not be working for your use case. If something is not working as expected, or it is missing that certain feature to make it work for you, feel free to create an issue in the GitHub repository.