Link back http response to its http request in a concurrent execution

I am working on a C# Web API that performs a specific action using a third-party-api-1, executed concurrently for speed. Once I get my output from the third-party-api-1, I would further get additional processing using the third-party-api-2, which is again intended to be run concurrently, and its results would be appended to the results from third-party-api-1, and eventually the output from my API would be sent back to the caller.

So the path is:

1. My API receives input
2. My API calls third-party-api-1 concurrently, which I intend to keep for speed
3. My API calls third-party-api-2, again wanting to keep it concurrent execution

I would like to identify my http requests after the calls to third-party-api-1 and third-party-api-2 are done so that I can tie back the outputs to input and return the result to the caller. If I had any control over third-party-api-1 & 2, I would have set some correlation-ids in the request header and persisted in the response too, but I can't do that with my third party APIs.

My issue is that once I construct my http get requests into a concurrent mode, I am no longer able to link back each response to its original request.

Is there any way to achieve what I am trying to do? Or is my attempt futile or bad design all together?

// I build my get query inputs from my user requestforeach (ParsedInputAddress ia in inaddr){...     addresses.Add(addrbuilder.ToString());     addrbuilder.Clear();}.// I call the http concurrentlyIEnumerable<Task<HttpResponseMessage>> getTasks = addresses.Select(async ia => await httpClient.GetAsync(basepath + ia.ToString()));var gets = await Task.WhenAll(getTasks);//this tasks will run concurrentlyforeach (var getContent in gets){     jsonResponse = await getContent.Content.ReadAsStringAsync();     if (jsonResponse != null)         vaddr = JsonSerializer.Deserialize<ValidatedAddress>(jsonResponse);     if (vaddr != null && vaddr.address != null)         vaddresses.Add(vaddr.address);}

I tried to set custom http request with an unique GUID but since I do not have control over third-party-api, I am unable to receive that ID in the response to tie them together.

My last resort is to make this a non-concurrent execution so that each request is processed by API-1 and 2 sequentially, preserving the link between request and response.