搭建消息告警模块以及跨网推送服务，支持企微，飞书，钉钉通知

Common/Notify/ImWebhookSigner.cs

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+using System.Security.Cryptography;
+using System.Text;
+
+namespace Common.Notify
+{
+    /// <summary>
+    /// IM 机器人 Webhook 加签工具（钉钉/飞书）
+    /// 供 IOT_API 直连推送与 AlertBridge 跨网转发程序共用，保证两种模式签名算法一致
+    /// </summary>
+    public static class ImWebhookSigner
+    {
+        /// <summary>
+        /// 钉钉机器人加签：sign = UrlEncode(Base64(HmacSHA256(timestamp + "\n" + secret, key=secret)))
+        /// </summary>
+        /// <param name="timestampMs">毫秒时间戳</param>
+        /// <param name="secret">加签密钥（SEC 开头）</param>
+        /// <returns>URL 编码后的签名</returns>
+        public static string DingTalkSign(long timestampMs, string secret)
+        {
+            string stringToSign = $"{timestampMs}\n{secret}";
+            using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(secret));
+            byte[] signData = hmac.ComputeHash(Encoding.UTF8.GetBytes(stringToSign));
+            return Uri.EscapeDataString(Convert.ToBase64String(signData));
+        }
+
+        /// <summary>
+        /// 飞书机器人加签：sign = Base64(HmacSHA256(空串, key=timestamp + "\n" + secret))
+        /// 注意与钉钉相反：飞书以"时间戳\n密钥"为 key、对空内容签名
+        /// </summary>
+        /// <param name="timestampSec">秒级时间戳</param>
+        /// <param name="secret">加签密钥</param>
+        /// <returns>Base64 签名</returns>
+        public static string FeishuSign(long timestampSec, string secret)
+        {
+            using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes($"{timestampSec}\n{secret}"));
+            byte[] signData = hmac.ComputeHash(Array.Empty<byte>());
+            return Convert.ToBase64String(signData);
+        }
+    }
+}