curl 'https://oapi.dingtalk.com/robot/send"msgtype": "text", 
 "text": {
  "content": "我就是我, 是不一样的烟火"
  }
 }'

/// <summary>
/// 钉钉群机器人消息类型枚举
/// </summary>
public enum MsgTypeEnum
{
 text,
 link,
 markdown,
 actionCard,
 feedCard
}

/// <summary>
/// 文本类型
/// </summary>
public class Text
{
 /// <summary>
 /// 文本内容
 /// </summary>
 [JsonProperty(PropertyName = "content")]
 public string Content { get; set; }
}

/// <summary>
/// @指定人
/// </summary>
public class At
{
 /// <summary>
 /// @的联系人
 /// </summary>
 [JsonProperty(PropertyName = "atMobiles")]
 public List<string> AtMobiles { set; get; }

 /// <summary>
 /// 是否@所有人
 /// </summary>
 [JsonProperty(PropertyName = "isAtAll")]
 public bool IsAtAll { set; get; }
}

/// <summary>
/// 发送钉钉消息接口
/// </summary>
[Route("api/[controller]")]
[ApiController]
public class DingTalkController : ControllerBase
{
 private readonly string WebHook_Token = "https://oapi.dingtalk.com/robot/send";

 private readonly IHttpClientFactory _httpClientFactory;

 public DingTalkController(IHttpClientFactory httpClientFactory)
 {
  _httpClientFactory = httpClientFactory;
 }
}

/// <summary>
/// 调用钉钉机器人发送文本内容
/// </summary>
/// <returns></returns>
[HttpGet]
[Route(nameof(TextContent))]
public async Task<ActionResult> TextContent()
{
 //消息类型
 var msgtype = MsgTypeEnum.text.ToString();

 //文本内容
 var text = new Text
 {
  Content = "看万山红遍，层林尽染；漫江碧透，百舸争流@15675120617"
 };

 //指定目标人群
 var at = new At()
 {
  AtMobiles = new List<string>() { "15675120617" },
  IsAtAll = false
 };

 var response = await SendDingTalkMessage(new { msgtype, text, at });

 return Ok(response);
}

/// <summary>
/// 执行发送消息
/// </summary>
/// <param name="sendMessage"></param>
/// <returns></returns>
private async Task<HttpResponseMessage> SendDingTalkMessage(object value)
{
 var sendMessage = JsonConvert.SerializeObject(value);

 var request = new HttpRequestMessage(HttpMethod.Post, WebHook_Token)
 {
  //钉钉文档需指定UTF8编码
  Content = new StringContent(sendMessage, Encoding.UTF8, "application/json")
 };

 var client = _httpClientFactory.CreateClient();
 var response = await client.SendAsync(request);

 return response;
}