Add read:metrics scope for metrics endpoint

and ensure token auth is accepted

jupyterhub/utils.py

@@ -320,9 +320,11 @@ def admin_only(f):
 @auth_decorator
 def metrics_authentication(self):
     """Decorator for restricting access to metrics"""
-    user = self.current_user
-    if user is None and self.authenticate_prometheus:
-        raise web.HTTPError(403)
+    if not self.authenticate_prometheus:
+        return
+    scope = 'read:metrics'
+    if scope not in self.parsed_scopes:
+        raise web.HTTPError(403, f"Access to metrics requires scope '{scope}'")
 
 
 # Token utilities