What is the URL for configuring OAuth2 services?
You enable OAuth2 authentication in admin/structure/services/list/$yourserver, then on the Authentication tab (admin/structure/services/list/$yourserver/authentication) you select the OAuth2 server.
After that, once you go to the Resources tab (admin/structure/services/list/$yourserver/resources) you will see the mentioned settings in the Settings column for each resource.

Make sure that you have the latest -dev release of Services, or the patch mentioned on the OAuth2 Server project page applied, otherwise it won't work.