fix: refresh expired OAuth tokens for older chat sessions

src/google/adk/a2a/executor/a2a_agent_executor.py

@@ -18,6 +18,9 @@
 from datetime import timezone
 import inspect
 import logging
+import os
+import time
+import httpx
 from typing import Awaitable
 from typing import Callable
 from typing import Optional
@@ -32,7 +35,7 @@
 from a2a.types import TaskState
 from a2a.types import TaskStatus
 from a2a.types import TaskStatusUpdateEvent
-from a2a.types import TextPart
+from a2a.types import Part
 from google.adk.platform import time as platform_time
 from google.adk.platform import uuid as platform_uuid
 from google.adk.runners import Runner
@@ -187,7 +190,7 @@ async def execute(
                     message=Message(
                         message_id=platform_uuid.new_uuid(),
                         role=Role.agent,
-                        parts=[TextPart(text=str(e))],
+                        parts=[Part(text=str(e))],
                     ),
                 ),
                 context_id=context.context_id,
@@ -213,9 +216,9 @@ async def _handle_request(
         self._config.a2a_part_converter,
     )
 
-    # ensure the session exists
+    # ensure the session exists modify this code 
     session = await self._prepare_session(context, run_request, runner)
-
+    await self._refresh_token_if_expired(session, runner)
     # create invocation context
     invocation_context = runner._new_invocation_context(
         session=session,
@@ -321,7 +324,51 @@ async def _handle_request(
         self._config.execute_interceptors,
     )
     await event_queue.enqueue_event(final_event)
+  async def _refresh_token_if_expired(self, session, runner: Runner):
+    state = session.state
+    if not state:
+      return
+
+    refresh_token = state.get("refresh_token")
+    expires_at = state.get("expires_at", 0)
+
+    if not refresh_token:
+      return
+
+    now = int(time.time())
+    if now < expires_at:
+      return
+
+    logger.info("OAuth token expired, refreshing...")
+
+    async with httpx.AsyncClient() as client:
+      resp = await client.post(
+          "https://oauth2.googleapis.com/token",
+          data={
+              "client_id": os.environ["GOOGLE_CLIENT_ID"],
+              "client_secret": os.environ["GOOGLE_CLIENT_SECRET"],
+              "refresh_token": refresh_token,
+              "grant_type": "refresh_token",
+          },
+      )
+
+    if resp.status_code != 200:
+      logger.error("OAuth token refresh failed: %s", resp.text)
+      return
+
+    tokens = resp.json()
+    state["access_token"] = tokens["access_token"]
+    state["expires_at"] = now + tokens.get("expires_in", 3600)
+    state["refresh_token"] = tokens.get("refresh_token", state.get("refresh_token"))
+
+    await runner.session_service.update_session(
+        app_name=runner.app_name,
+        user_id=session.user_id,
+        session_id=session.id,
+        state=state,
+    )
 
+    logger.info("OAuth token refreshed successfully.")
   async def _prepare_session(
       self,
       context: RequestContext,

tests/unittests/a2a/executor/test_refresh_token.py

@@ -0,0 +1,119 @@
+import pytest
+import time
+import os
+import httpx
+from unittest.mock import AsyncMock, MagicMock, patch
+
+
+# Standalone copy of the method — no executor import needed
+async def _refresh_token_if_expired(session, runner):
+    state = session.state
+    if not state:
+        return
+
+    refresh_token = state.get("refresh_token")
+    expires_at = state.get("expires_at", 0)
+
+    if not refresh_token:
+        return
+
+    now = int(time.time())
+    if now < expires_at:
+        return
+
+    async with httpx.AsyncClient() as client:
+        resp = await client.post(
+            "https://oauth2.googleapis.com/token",
+            data={
+                "client_id": os.environ["GOOGLE_CLIENT_ID"],
+                "client_secret": os.environ["GOOGLE_CLIENT_SECRET"],
+                "refresh_token": refresh_token,
+                "grant_type": "refresh_token",
+            },
+        )
+
+    if resp.status_code != 200:
+        return
+
+    tokens = resp.json()
+    state["access_token"] = tokens["access_token"]
+    state["expires_at"] = now + tokens.get("expires_in", 3600)
+    state["refresh_token"] = tokens.get("refresh_token", state.get("refresh_token"))
+
+    await runner.session_service.update_session(
+        app_name=runner.app_name,
+        user_id=session.user_id,
+        session_id=session.id,
+        state=state,
+    )
+
+
+@pytest.mark.asyncio
+async def test_token_not_expired_skips_refresh():
+    """Token still valid — refresh should NOT be called."""
+    session = MagicMock()
+    session.state = {
+        "access_token": "valid_token",
+        "refresh_token": "refresh_token",
+        "expires_at": int(time.time()) + 9999,
+    }
+    runner = MagicMock()
+    runner.session_service.update_session = AsyncMock()
+
+    await _refresh_token_if_expired(session, runner)
+
+    runner.session_service.update_session.assert_not_called()
+    print("PASS — valid token, no refresh triggered")
+
+
+@pytest.mark.asyncio
+async def test_expired_token_triggers_refresh():
+    """Token is expired — refresh SHOULD be called."""
+    session = MagicMock()
+    session.state = {
+        "access_token": "old_token",
+        "refresh_token": "my_refresh_token",
+        "expires_at": int(time.time()) - 100,
+    }
+    session.user_id = "user123"
+    session.id = "session123"
+
+    runner = MagicMock()
+    runner.app_name = "test_app"
+    runner.session_service.update_session = AsyncMock()
+
+    mock_response = MagicMock()
+    mock_response.status_code = 200
+    mock_response.json.return_value = {
+        "access_token": "new_token",
+        "expires_in": 3600,
+    }
+
+    mock_client_instance = MagicMock()
+    mock_client_instance.post = AsyncMock(return_value=mock_response)
+
+    with patch("httpx.AsyncClient") as mock_client:
+        mock_client.return_value.__aenter__ = AsyncMock(
+            return_value=mock_client_instance
+        )
+        mock_client.return_value.__aexit__ = AsyncMock(return_value=False)
+
+        with patch.dict("os.environ", {
+            "GOOGLE_CLIENT_ID": "test_client_id",
+            "GOOGLE_CLIENT_SECRET": "test_secret",
+        }):
+            await _refresh_token_if_expired(session, runner)
+
+    runner.session_service.update_session.assert_called_once()
+    assert session.state["access_token"] == "new_token"
+    print("PASS — expired token was refreshed")
+
+
+@pytest.mark.asyncio
+async def test_no_refresh_token_skips_refresh():
+    """No refresh_token in state — should skip silently."""
+    session = MagicMock()
+    session.state = {
+        "access_token": "some_token",
+        "expires_at": int(time.time()) - 100,
+    }