[Frontend] Apply request header overrides to chat completions (#35001)

Co-authored-by: Ye (Charlotte) Qi <ye.charlotte.qi@gmail.com>

python/sglang/srt/entrypoints/openai/serving_chat.py

@@ -61,6 +61,7 @@ from sglang.srt.entrypoints.openai.utils import (
     should_include_usage,
     to_openai_style_logprobs,
 )
+from sglang.srt.entrypoints.request_headers import apply_header_overrides
 from sglang.srt.environ import envs
 from sglang.srt.function_call.core_types import ToolCallItem
 from sglang.srt.function_call.function_call_parser import FunctionCallParser
@@ -1037,6 +1038,11 @@ class OpenAIServingChat(OpenAIServingBase):
             return_prompt_token_ids=request.return_prompt_token_ids
             or request.return_token_ids,
         )
+        if (
+            raw_request is not None
+            and envs.SGLANG_ENABLE_REQUEST_HEADER_OVERRIDES.get()
+        ):
+            apply_header_overrides(adapted_request, raw_request.headers)
 
         return adapted_request, request