Provide a way to explicitly look for consumer id, username, or custom id as authentication method.

[rucciva]

Some deployment might use internal oauth2 provider that they trust and control, so they can safely assume that consumer id, username, or custom id is stored safely and appropriately. WIth this feature, they don't need to create credential and associate it with the 3rd party oauth2 client id.

Though if this feature is implemented, it has little correlation with audience claim (and the plugin name).