为何HttpClient.CancelPendingRequests无法在WebApp中取消待处理请求？

我在ASP.NET Core Web应用中尝试实现服务器端HTTP请求取消功能，基于WeatherForecast示例搭建了演示项目。客户端通过HttpClient发起请求，服务端注入CancellationToken并注册取消逻辑，循环生成数据并延迟执行。调用CancelPendingRequests尝试取消请求时，服务端的CancellationToken无法检测到取消信号；但相同的取消代码在Blazor和.NET桌面客户端中能正常中断服务端处理。

客户端代码 #

public async Task<IActionResult> OnGet()
{
    string uri = "http://localhost:5031/weatherforecast";
    _requestTask = _httpClient.GetFromJsonAsync<IEnumerable<WeatherForecast>>(uri);

    IEnumerable<WeatherForecast>? forecasts = await _requestTask;
    _requestTask = null;

    ViewData["WeatherForecastData"] = forecasts;

    return Page();
}

服务端代码 #

[HttpGet]
public async Task<IEnumerable<WeatherForecast>> Get(CancellationToken cancellationToken)
{
    bool cancel = false;
    cancellationToken.Register(() => {
        cancel = true;
    });

    int count = 5;
    List<WeatherForecast> ret = new List<WeatherForecast>();
    for (int i = 1; i <= count; i++)
    {
        Debug.WriteLine($"Iter #{i}");
        if (cancel) // (cancellationToken.IsCancellationRequested)
        {
            Debug.WriteLine("Cancelled");
            throw new Exception($"Canceled after {i} forecast items");
        }
        await Task.Delay(1000);
        WeatherForecast wf = new WeatherForecast()
        {
            Date = DateTime.Now.AddDays(i),
            TemperatureC = Random.Shared.Next(-20, 55),
            Summary = Summaries[Random.Shared.Next(Summaries.Length)]
        };
        ret.Add(wf);
    }

    return ret;
}

客户端取消代码 #

public void OnPostCancel ()
{
    //cts.Cancel();
    _httpClient.CancelPendingRequests();
    ViewData["WeatherForecastData"] = new List<WeatherForecast>();
}

内容的提问来源于stack exchange，提问作者Greg Arzoomanian