This document is still not complete.
Most topics on OAuth2 Authentication are very similar to the ones described in ADFS Authentication via OAuth2.
The most important thing for a generic OAuth2 setup to work is that wicked assumes the Access Token being returned after successfully authenticating/authorizing with your OAuth2 Identity Provider is a JWT (JSON Web Token), containing the user profile of the user.
The auth method oauth2 allows mapping different properties/claims from the JWT into the wicked profile. The JWT must always contain valid claims for sub (unique ID) and email. The generic oauth2 auth method also supports mapping user groups (in case they are transferred) to wicked user groups, just like for the ADFS case.
As an alternative, the oauth2 auth method allows retrieving a profile from an OIDC style /user_info end point. Also in case this possibility is used, the retrieved profile must contain at least the properties sub (as a unique ID) and email.