C#提交http post请求以填写表单

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading.Tasks;

class Program
{
    static async Task Main(string[] args)
    {
        // 创建HttpClient实例
        using (HttpClient client = new HttpClient())
        {
            // 构造表单数据
            var formContent = new FormUrlEncodedContent(new[]
            {
                new KeyValuePair<string, string>("username", "John"),
                new KeyValuePair<string, string>("password", "123456")
            });

            // 发送POST请求
            HttpResponseMessage response = await client.PostAsync("https://example.com/login", formContent);

            // 检查响应状态码
            if (response.IsSuccessStatusCode)
            {
                // 处理成功响应
                string result = await response.Content.ReadAsStringAsync();
                Console.WriteLine("登录成功：" + result);
            }
            else
            {
                // 处理错误响应
                Console.WriteLine("登录失败：" + response.StatusCode);
            }
        }
    }
}