当使用 HttpClient 与外部资源通信时，需要手动跟踪请求的相关性。为了在 Application Insights 中呈现相关性，需要使用 IHttpContextAccessor 接口来收集传递给其他服务和 API 的每个请求的唯一标识符，并将其添加到 HttpClient 请求头中。这可以通过以下代码实现：

using Microsoft.ApplicationInsights;
using Microsoft.AspNetCore.Http;
using System.Net.Http;
using System.Threading.Tasks;

public class MyHttpClient : IMyHttpClient
{
    private readonly HttpClient _httpClient;
    private readonly IHttpContextAccessor _httpContextAccessor;
    private readonly TelemetryClient _telemetryClient;

    public MyHttpClient(HttpClient httpClient,
        IHttpContextAccessor httpContextAccessor,
        TelemetryClient telemetryClient)
    {
        _httpClient = httpClient;
        _httpContextAccessor = httpContextAccessor;
        _telemetryClient = telemetryClient;
    }

    public async Task GetAsync(string uri)
    {
        // Create a new HttpRequestMessage and add the correlation ID to its headers
        var httpRequestMessage = new HttpRequestMessage(HttpMethod.Get, uri);
        httpRequestMessage.Headers.Add("x-correlation-id", _httpContextAccessor.HttpContext.TraceIdentifier);

        // Start a new telemetry operation to track the HTTP request
        using (var operation = _telemetryClient.StartOperation("MyHttpClient.GetAsync"))
        {
            try
            {
                // Send the HTTP request and get the response
                var response = await _httpClient.SendAsync(httpRequestMessage);
                operation.Telemetry.ResultCode = response.StatusCode.ToString();
                return response;
            }
            catch (HttpRequestException ex)
            {
                operation.Telemetry.Success = false;
                operation.Telemetry.ResultCode = ex.StatusCode?.ToString();
                _telemetryClient.TrackException(ex);
                throw;
            }
        }
    }
}

在此示例中，我们创建了一个名为 MyHttpClient 的类，该类使用 IHttpContextAccessor 接口来收集每个请求的唯一标识符并将其添加到 HttpClient 请求头中。我们还使用 TelemetryClient 开始新的操作以跟踪 HTTP 请求，以便可以