Correct Way To Return HttpResponseMessage As IActionResult In .Net Core 2.2

Answer :

public class HttpResponseMessageResult : IActionResult
{
    private readonly HttpResponseMessage _responseMessage;

    public HttpResponseMessageResult(HttpResponseMessage responseMessage)
    {
        _responseMessage = responseMessage; // could add throw if null
    }

    public async Task ExecuteResultAsync(ActionContext context)
    {
        var response = context.HttpContext.Response;


        if (_responseMessage == null)
        {
            var message = "Response message cannot be null";

            throw new InvalidOperationException(message);
        }

        using (_responseMessage)
        {
            response.StatusCode = (int)_responseMessage.StatusCode;

            var responseFeature = context.HttpContext.Features.Get<IHttpResponseFeature>();
            if (responseFeature != null)
            {
                responseFeature.ReasonPhrase = _responseMessage.ReasonPhrase;
            }

            var responseHeaders = _responseMessage.Headers;

            // Ignore the Transfer-Encoding header if it is just "chunked".
            // We let the host decide about whether the response should be chunked or not.
            if (responseHeaders.TransferEncodingChunked == true &&
                responseHeaders.TransferEncoding.Count == 1)
            {
                responseHeaders.TransferEncoding.Clear();
            }

            foreach (var header in responseHeaders)
            {
                response.Headers.Append(header.Key, header.Value.ToArray());
            }

            if (_responseMessage.Content != null)
            {
                var contentHeaders = _responseMessage.Content.Headers;

                // Copy the response content headers only after ensuring they are complete.
                // We ask for Content-Length first because HttpContent lazily computes this
                // and only afterwards writes the value into the content headers.
                var unused = contentHeaders.ContentLength;

                foreach (var header in contentHeaders)
                {
                    response.Headers.Append(header.Key, header.Value.ToArray());
                }

                await _responseMessage.Content.CopyToAsync(response.Body);
            }
        }
    }

You can create a custom IActionResult that will wrap transfere logic.

public async Task<IActionResult> Routes([FromBody]JObject request)
{
    var httpClient = new HttpClient();

    HttpResponseMessage response = await httpClient.GetAsync("");

    // Here we ask the framework to dispose the response object a the end of the user resquest
    this.HttpContext.Response.RegisterForDispose(response);

    return new HttpResponseMessageResult(response);
}

public class HttpResponseMessageResult : IActionResult
{
    private readonly HttpResponseMessage _responseMessage;

    public HttpResponseMessageResult(HttpResponseMessage responseMessage)
    {
        _responseMessage = responseMessage; // could add throw if null
    }

    public async Task ExecuteResultAsync(ActionContext context)
    {
        context.HttpContext.Response.StatusCode = (int)_responseMessage.StatusCode;

        foreach (var header in _responseMessage.Headers)
        {
            context.HttpContext.Response.Headers.TryAdd(header.Key, new StringValues(header.Value.ToArray()));
        }

        using (var stream = await _responseMessage.Content.ReadAsStreamAsync())
        {
            await stream.CopyToAsync(context.HttpContext.Response.Body);
            await context.HttpContext.Response.Body.FlushAsync();
        }
    }
}