### Describe the bug When converting OpenAPI Spec to MCP toolset via LiteLLM proxy (version v1.91.0), the extra_headers configured under the OpenAPI-derived MCP server entry fail to be injected & passed through to the final upstream backend API request. ### Expected behavior Define an MCP server from OpenAPI spec in config.yaml with extra_headers: ["Authorization", "X-Tenant-ID"] MCP client sends request with allowed forwarded headers LiteLLM forwards these headers to the target backend API defined in OpenAPI spec ### Actual behavior LiteLLM receives inbound headers correctly (verified via DEBUG log & x-litellm-mcp-debug: true response headers) Headers are stripped before dispatching HTTP request to upstream OpenAPI backend service Upstream API never receives the configured extra headers, resulting in 401/403 missing auth context ### Reproduction steps 1. Deploy litellm proxy v1.91.0 Minimal config.yaml snippet: ```yaml model_list: - model_name: openapi-mcp-demo litellm_params: custom_llm_provider: openapi_mcp openapi_spec: "https://xxx/service-openapi.yaml" extra_headers: ["Authorization", "X-Tenant-ID"] api_base: "https://backend-api.example.com" ```…