fix(vertex_httpx.py): allow passing extra headers

Closes https://github.com/BerriAI/litellm/pull/4327

litellm/llms/vertex_httpx.py

@@ -775,6 +775,8 @@ class VertexLLM(BaseLLM):
         }
         if auth_header is not None:
             headers["Authorization"] = f"Bearer {auth_header}"
+        if extra_headers is not None:
+            headers.update(extra_headers)
 
         ## LOGGING
         logging_obj.pre_call(

litellm/main.py

@@ -1931,6 +1931,7 @@ def completion(
                 custom_llm_provider=custom_llm_provider,
                 client=client,
                 api_base=api_base,
+                extra_headers=extra_headers,
             )
 
         elif custom_llm_provider == "vertex_ai":

litellm/tests/test_amazing_vertex_completion.py

@@ -877,6 +877,7 @@ async def test_gemini_pro_httpx_custom_api_base(provider):
                 response_format={"type": "json_object"},
                 client=client,
                 api_base="my-custom-api-base",
+                extra_headers={"hello": "world"},
             )
         except Exception as e:
             pass
@@ -884,6 +885,7 @@ async def test_gemini_pro_httpx_custom_api_base(provider):
         mock_call.assert_called_once()
 
         assert "my-custom-api-base:generateContent" == mock_call.call_args.kwargs["url"]
+        assert "hello" in mock_call.call_args.kwargs["headers"]
 
 
 @pytest.mark.skip(reason="exhausted vertex quota. need to refactor to mock the call")