https://docs.mongodb.com/ruby-driver/current/tutorials/ruby-driver-authentication/ should focus on how to authenticate via various mechanisms, but it starts by showing how to create a user. In practice if one creates users one also needs to list existing users, find out their roles, and remove users. User management should be a separate page from authentication and should detail how to perform various operations on users that the driver does provide convenient methods for, and possibly cover roles as well.