通过Selvin的回复，我想出了一个办法：

        private string Post(string url,ByteArrayContent content,AuthenticationToken token = null) {
            return this.Send(token,(client) => client.PostAsync(url,content));
        }

        private string Put(string url,StringContent content,AuthenticationToken token) {
            return this.Send(token,(client) => client.PutAsync(url,content));
        }

        private string Send(AuthenticationToken token,Func<HttpClient,Task<HttpResponseMessage>> sendFunction) {
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

            using HttpClient client = new HttpClient();
            if (token != null) {
                client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer",token.Access_token);
            }

            return sendFunction(client)
                .Result.Content.ReadAsStringAsync()
                .Result;
        }

...这几乎是我想要的，但是我仍然需要两次表达“客户”。

C＃是否有任何符号可以让我删除此冗余？

还是我应该接受它为“效果最好”？

我认为由于某些原因您不能使用async/await运算符，

您可以这样减少冗余：

    public static class Ext
    {
        public static string Finalize(this Task<HttpResponseMessage> httpResponseMessage)
        {
            return httpResponseMessage
                .Result
                .Content
                .ReadAsStringAsync()
                .Result;
        }
    }

    public class Program
    {
        private string Post(string url,AuthenticationToken token = null)
        {
            return this.CreateClient(token)
                .PutAsync(url,content)
                .Finalize();
        }

        private string Put(string url,AuthenticationToken token)
        {
            return this.CreateClient(token)
                .PostAsync(url,content)
                .Finalize();
        }

        private HttpClient CreateClient(AuthenticationToken token)
        {

            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

            using HttpClient client = new HttpClient();
            if (token != null)
            {
                client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer",token.Value);
            }

            return client;
        }
    }

因此，将“客户端创建”包装在一种方法中，然后将“完成异步处理”包装到扩展方法中

您可以使用switch表达式。它在C＃8中变得惊人地起作用。您可以在此处阅读更多内容并找到示例：

https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#switch-expressions

更新：考虑使用枚举而不是函数名称来确保代码类型安全。