feat(apigee): add userinfo.email scope for tokeninfo user identification

ApigeeLlm now explicitly requests the userinfo.email OAuth scope
alongside cloud-platform when creating credentials. This enables
Apigee Gateway to identify callers via Google's tokeninfo API when
using Service Account key authentication.

Fixes #4721

Author: polar3130

src/google/adk/models/apigee_llm.py

@@ -29,6 +29,7 @@
 from typing import Optional
 from typing import TYPE_CHECKING
 
+import google.auth
 from google.adk import version as adk_version
 from google.genai import types
 import httpx
@@ -52,6 +53,11 @@
 _PROJECT_ENV_VARIABLE_NAME = 'GOOGLE_CLOUD_PROJECT'
 _LOCATION_ENV_VARIABLE_NAME = 'GOOGLE_CLOUD_LOCATION'
 
+_APIGEE_SCOPES = [
+    'https://www.googleapis.com/auth/cloud-platform',
+    'https://www.googleapis.com/auth/userinfo.email',
+]
+
 _CUSTOM_METADATA_FIELDS = (
     'id',
     'created',
@@ -232,13 +238,16 @@ def api_client(self) -> Client:
         **kwargs_for_http_options,
     )
 
+    credentials, _ = google.auth.default(scopes=_APIGEE_SCOPES)
+
     kwargs_for_client = {}
     kwargs_for_client['vertexai'] = self._isvertexai
     if self._isvertexai:
       kwargs_for_client['project'] = self._project
       kwargs_for_client['location'] = self._location
 
     return Client(
+        credentials=credentials,
         http_options=http_options,
         **kwargs_for_client,
     )

tests/unittests/models/test_apigee_llm.py

@@ -18,6 +18,7 @@
 from unittest import mock
 from unittest.mock import AsyncMock
 
+from google.adk.models.apigee_llm import _APIGEE_SCOPES
 from google.adk.models.apigee_llm import ApigeeLlm
 from google.adk.models.apigee_llm import CompletionsHTTPClient
 from google.adk.models.llm_request import LlmRequest
@@ -627,3 +628,42 @@ async def test_api_key_injection_openai(model):
   )
   client = apigee_llm._completions_http_client
   assert client._headers['Authorization'] == 'Bearer sk-test-key'
+
+
+@pytest.mark.asyncio
+@mock.patch('google.genai.Client')
+@mock.patch('google.adk.models.apigee_llm.google.auth.default')
+async def test_api_client_requests_userinfo_email_scope(
+    mock_auth_default, mock_client_constructor, llm_request
+):
+  """Tests that api_client requests userinfo.email scope for Apigee Gateway tokeninfo."""
+  mock_credentials = mock.Mock()
+  mock_auth_default.return_value = (mock_credentials, 'test-project')
+
+  mock_client_instance = mock.Mock()
+  mock_client_instance.aio.models.generate_content = AsyncMock(
+      return_value=types.GenerateContentResponse(
+          candidates=[
+              types.Candidate(
+                  content=Content(
+                      parts=[Part.from_text(text='Test response')],
+                      role='model',
+                  )
+              )
+          ]
+      )
+  )
+  mock_client_constructor.return_value = mock_client_instance
+
+  apigee_llm = ApigeeLlm(
+      model=APIGEE_GEMINI_MODEL_ID,
+      proxy_url=PROXY_URL,
+  )
+  _ = [resp async for resp in apigee_llm.generate_content_async(llm_request)]
+
+  mock_auth_default.assert_called_once_with(scopes=_APIGEE_SCOPES)
+  assert 'https://www.googleapis.com/auth/userinfo.email' in _APIGEE_SCOPES
+  assert 'https://www.googleapis.com/auth/cloud-platform' in _APIGEE_SCOPES
+
+  _, kwargs = mock_client_constructor.call_args
+  assert kwargs['credentials'] is mock_credentials