Can’t pass per-request headers like Authorization using from_openapi

[JoeyKoetting]

I’m trying to use FastMCP.from_openapi to build a server from an OpenAPI spec, but I can’t figure out how to forward per-request headers (like Authorization or Cookie) from the MCP client.

The headers parameter on from_openapi only supports static headers, which doesn’t work in a multi-user setup. Ideally, the MCP client would send headers and the server would forward them for each request, but I haven’t found a way to do that with from_openapi.

Here’s the basic setup:

mcp = FastMCP.from_openapi(
    openapi_spec=openapi_spec,
    client=api_client,
    name="OpenAPI Server",
    # headers=headers  # not useful here since they're static
)

I’ve worked around this by creating a manual tool like this:

@mcp.tool()
async def v1_manual_tool(ctx: Context, uuid: str):
    headers = ctx.get_http_request().headers
    api_headers = {
        "Authorization": headers.get("Authorization"),
        "Cookie": headers.get("Cookie"),
        ...
    }
    api_client = httpx.AsyncClient(base_url="http://127.0.0.1:8000/", headers=api_headers)
    response = await api_client.delete(f"/api/v1/someUrl/")
    await api_client.aclose()
    return response.json()

But this feels like a hack, and it defeats the point of using from_openapi.
Is there a built-in or recommended way to propagate client headers dynamically?

[jlowin]

That's an excellent point. I've turned this into #346

[JoeyKoetting]

Appreciate the help! Good to know I wasn't missing something.