From 202bc371d118dd827b26f01d1cae0b52fb320295 Mon Sep 17 00:00:00 2001
From: Yufeng He <40085740+universeplayer@users.noreply.github.com>
Date: Thu, 23 Apr 2026 12:16:26 +0800
Subject: [PATCH] Python: fix FoundryChatClient/FoundryAgent dropping
 default_headers

default_headers was accepted by the constructor and stored on the
instance but never forwarded to the AsyncOpenAI client obtained from
AIProjectClient.get_openai_client(), so custom headers never reached
outbound requests.

Forward default_headers through get_openai_client(**kwargs) -- the
Azure SDK already supports this kwarg and passes it on to AsyncOpenAI.

Added two regression tests and updated the mock-based header test so
we cover both the stored-attribute path and the actually-forwarded
path.

Fixes #5416.
---
 .../foundry/agent_framework_foundry/_agent.py |  5 ++-
 .../agent_framework_foundry/_chat_client.py   |  6 ++-
 .../tests/foundry/test_foundry_chat_client.py | 37 +++++++++++++++++++
 3 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/python/packages/foundry/agent_framework_foundry/_agent.py b/python/packages/foundry/agent_framework_foundry/_agent.py
index 0c7f93ba1f..09dba4743a 100644
--- a/python/packages/foundry/agent_framework_foundry/_agent.py
+++ b/python/packages/foundry/agent_framework_foundry/_agent.py
@@ -198,7 +198,10 @@ def __init__(
             self._should_close_client = True
 
         # Get OpenAI client from project
-        async_client = self.project_client.get_openai_client()
+        openai_client_kwargs: dict[str, Any] = {}
+        if default_headers:
+            openai_client_kwargs["default_headers"] = dict(default_headers)
+        async_client = self.project_client.get_openai_client(**openai_client_kwargs)
 
         super().__init__(
             async_client=async_client,
diff --git a/python/packages/foundry/agent_framework_foundry/_chat_client.py b/python/packages/foundry/agent_framework_foundry/_chat_client.py
index 7c9eb3a68c..021b29edb5 100644
--- a/python/packages/foundry/agent_framework_foundry/_chat_client.py
+++ b/python/packages/foundry/agent_framework_foundry/_chat_client.py
@@ -204,9 +204,13 @@ def __init__(
                 project_client_kwargs["allow_preview"] = allow_preview
             project_client = AIProjectClient(**project_client_kwargs)
 
+        openai_client_kwargs: dict[str, Any] = {}
+        if default_headers:
+            openai_client_kwargs["default_headers"] = dict(default_headers)
+
         super().__init__(
             model=resolved_model,
-            async_client=project_client.get_openai_client(),
+            async_client=project_client.get_openai_client(**openai_client_kwargs),
             default_headers=default_headers,
             instruction_role=instruction_role,
             compaction_strategy=compaction_strategy,
diff --git a/python/packages/foundry/tests/foundry/test_foundry_chat_client.py b/python/packages/foundry/tests/foundry/test_foundry_chat_client.py
index a7c5beb822..9e519b10c7 100644
--- a/python/packages/foundry/tests/foundry/test_foundry_chat_client.py
+++ b/python/packages/foundry/tests/foundry/test_foundry_chat_client.py
@@ -180,6 +180,43 @@ def test_init_with_default_header() -> None:
         assert client.default_headers[key] == value
 
 
+def test_default_headers_forwarded_to_openai_client() -> None:
+    """Regression: ``default_headers`` must be forwarded to the underlying AsyncOpenAI client.
+
+    Previously, ``FoundryChatClient(default_headers=...)`` stored the headers on the instance
+    but called ``project_client.get_openai_client()`` without forwarding them, so the headers
+    never reached outbound HTTP requests.
+    """
+    default_headers = {"x-custom-header": "repro-value"}
+    mock_openai_client = _make_mock_openai_client()
+    project_client = MagicMock()
+    project_client.get_openai_client.return_value = mock_openai_client
+
+    FoundryChatClient(
+        project_client=project_client,
+        model=_TEST_FOUNDRY_MODEL,
+        default_headers=default_headers,
+    )
+
+    project_client.get_openai_client.assert_called_once()
+    forwarded = project_client.get_openai_client.call_args.kwargs.get("default_headers")
+    assert forwarded is not None
+    for key, value in default_headers.items():
+        assert forwarded.get(key) == value
+
+
+def test_get_openai_client_not_called_with_headers_kwarg_when_unset() -> None:
+    """When ``default_headers`` is not passed, don't inject an empty dict into the Azure call."""
+    mock_openai_client = _make_mock_openai_client()
+    project_client = MagicMock()
+    project_client.get_openai_client.return_value = mock_openai_client
+
+    FoundryChatClient(project_client=project_client, model=_TEST_FOUNDRY_MODEL)
+
+    project_client.get_openai_client.assert_called_once()
+    assert "default_headers" not in project_client.get_openai_client.call_args.kwargs
+
+
 def test_init_with_project_endpoint_creates_project_client() -> None:
     credential = MagicMock()
     mock_openai_client = _make_mock_openai_client()