fix: Initialize self._auth_config inside BaseAuthenticatedTool

So that we can access self._auth_config in McpTool for getting auth headers

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 856451693

src/google/adk/tools/base_authenticated_tool.py

@@ -66,6 +66,7 @@ class BaseAuthenticatedTool(BaseTool):
         name=name,
         description=description,
     )
+    self._auth_config = auth_config
 
     if auth_config and auth_config.auth_scheme:
       self._credentials_manager = CredentialManager(auth_config=auth_config)

tests/unittests/tools/test_base_authenticated_tool.py

@@ -90,6 +90,7 @@ class TestBaseAuthenticatedTool:
     assert tool.description == "Test description"
     assert tool._credentials_manager is not None
     assert tool._response_for_auth_required == unauthenticated_response
+    assert tool._auth_config == auth_config
 
   def test_init_with_no_auth_config(self):
     """Test initialization without auth_config."""
@@ -99,6 +100,7 @@ class TestBaseAuthenticatedTool:
     assert tool.description == "Test authenticated tool"
     assert tool._credentials_manager is None
     assert tool._response_for_auth_required is None
+    assert tool._auth_config is None
 
   def test_init_with_empty_auth_scheme(self):
     """Test initialization with auth_config but no auth_scheme."""