Fix and templatize the logic for external JWT AuthN and registry v2 Auth.

Make it explicit that the registry-v2 stuff is not ready for prime time.

endpoints/v2/__init__.py

@@ -1,3 +1,6 @@
+# XXX This code is not yet ready to be run in production, and should remain disabled until such
+# XXX time as this notice is removed.
+
 import logging
 
 from flask import Blueprint, make_response
@@ -25,7 +28,7 @@ def _require_repo_permission(permission_class, allow_public=False):
       permission = permission_class(namespace, repo_name)
       if (permission.can() or
           (allow_public and
-           model.repository_is_public(namespace, repo_name))):
+           model.repository.repository_is_public(namespace, repo_name))):
         return func(namespace, repo_name, *args, **kwargs)
       raise abort(401)
     return wrapped