The headers with same key are overwritten

Starlette responses adds cookies as headers with the same key. self.raw_headers.append((b"set-cookie", cookie_val.encode("latin-1")))

In your middleware handle outgoing request over writes the same key with only the last value.

        async def handle_outgoing_request(message: Message) -> None:
            if message['type'] == 'http.response.start':
                headers = {k.decode(): v.decode() for (k, v) in message['headers']}
                headers[self.header_name] = correlation_id.get()
                headers['Access-Control-Expose-Headers'] = self.header_name
                response_headers = Headers(headers=headers)
                message['headers'] = response_headers.raw
            await send(message)

[lakshaythareja]

https://github.com/snok/asgi-correlation-id/pull/25

[sondrelg]

v1.1.3 should be out within the next minute, so will consider this closed 👍