Connector: refresh token if needed before metadata exchange.

Fix issue #346 "Invalid token in metadata exchange"

Author: Juan Pablo Ugarte

google/cloud/alloydb/connector/connector.py

@@ -15,6 +15,8 @@
 from __future__ import annotations
 
 import asyncio
+from google.auth.credentials import TokenState
+from google.auth.transport import requests
 from functools import partial
 import socket
 import struct
@@ -258,6 +260,10 @@ def metadata_exchange(
  if enable_iam_auth:
  auth_type = connectorspb.MetadataExchangeRequest.AUTO_IAM
 
+ # Ensure token is fresh
+ if self._credentials.token_state != TokenState.FRESH:
+ self._credentials.refresh(requests.Request())
+
  # form metadata exchange request
  req = connectorspb.MetadataExchangeRequest(
  user_agent=f"{self._client._user_agent}", # type: ignore