refactor(wxads): 以拦截器形式重新实现自动生成 AgencyToken 的逻辑

src/SKIT.FlurlHttpClient.Wechat.Ads/Interceptors/WechatAdsAgencyTokenInterceptor.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Flurl;
+using Flurl.Http;
+
+namespace SKIT.FlurlHttpClient.Wechat.Ads.Interceptors
+{
+    internal class WechatAdsAgencyTokenInterceptor : WechatHttpCallInterceptor
+    {
+        private readonly string _agencyId;
+        private readonly string _agencyApiKey;
+
+        public WechatAdsAgencyTokenInterceptor(string agencyId, string agencyApiKey)
+        {
+            _agencyId = agencyId;
+            _agencyApiKey = agencyApiKey;
+        }
+
+        public override async Task BeforeCallAsync(FlurlCall flurlCall)
+        {
+            if (flurlCall == null) throw new ArgumentNullException(nameof(flurlCall));
+
+            string timestamp = DateTimeOffset.Now.ToLocalTime().ToUnixTimeSeconds().ToString();
+            string nonce = Guid.NewGuid().ToString("N");
+            string sign = Security.MD5Utility.Hash($"{_agencyId}{timestamp}{nonce}{_agencyApiKey}").ToLower();
+            string token = Convert.ToBase64String(Encoding.UTF8.GetBytes($"{_agencyId},{timestamp},{nonce},{sign}"));
+
+            flurlCall.Request.RemoveQueryParam("agency_token");
+            flurlCall.Request.SetQueryParam("agency_token", token);
+
+            await Task.Yield();
+        }
+    }
+}