fix vertex only refresh auth when required

litellm/llms/vertex_ai_and_google_ai_studio/gemini/vertex_and_google_ai_studio_gemini.py

@@ -9,7 +9,17 @@ import types
 import uuid
 from enum import Enum
 from functools import partial
-from typing import Any, Callable, Dict, List, Literal, Optional, Tuple, Union
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Callable,
+    Dict,
+    List,
+    Literal,
+    Optional,
+    Tuple,
+    Union,
+)
 
 import httpx  # type: ignore
 import requests  # type: ignore
@@ -68,6 +78,11 @@ from .transformation import (
     sync_transform_request_body,
 )
 
+if TYPE_CHECKING:
+    from google.auth.credentials import Credentials as GoogleCredentialsObject
+else:
+    GoogleCredentialsObject = Any
+
 
 class VertexAIConfig:
     """
@@ -811,7 +826,7 @@ class VertexLLM(BaseLLM):
         super().__init__()
         self.access_token: Optional[str] = None
         self.refresh_token: Optional[str] = None
-        self._credentials: Optional[Any] = None
+        self._credentials: Optional[GoogleCredentialsObject] = None
         self.project_id: Optional[str] = None
         self.async_handler: Optional[AsyncHTTPHandler] = None
 
@@ -1139,7 +1154,8 @@ class VertexLLM(BaseLLM):
             if not self.project_id:
                 self.project_id = project_id or cred_project_id
         else:
-            self.refresh_auth(self._credentials)
+            if self._credentials.expired or not self._credentials.token:
+                self.refresh_auth(self._credentials)
 
             if not self.project_id:
                 self.project_id = self._credentials.project_id