Handle empty scopes and always send the WWW-Authenticate header, as per spec

Fixes #1045

endpoints/v2/tag.py

@@ -1,14 +1,14 @@
 from flask import jsonify, url_for
 
+from auth.registry_jwt_auth import process_registry_jwt_auth
 from endpoints.v2 import v2_bp, require_repo_read
 from endpoints.v2.errors import NameUnknown
 from endpoints.v2.v2util import add_pagination
-from auth.jwt_auth import process_jwt_auth
 from endpoints.decorators import anon_protect
 from data import model
 
 @v2_bp.route('/<namespace>/<repo_name>/tags/list', methods=['GET'])
-@process_jwt_auth
+@process_registry_jwt_auth
 @require_repo_read
 @anon_protect
 def list_all_tags(namespace, repo_name):