Update McpAuthenticationHandler.cs

Author: localden

src/ModelContextProtocol.AspNetCore/Authentication/McpAuthenticationHandler.cs

@@ -5,6 +5,7 @@
 using ModelContextProtocol.Authentication;
 using ModelContextProtocol.Utils.Json;
 using System.Text.Encodings.Web;
+using System.Text.Json;
 
 namespace ModelContextProtocol.AspNetCore.Authentication;
 
@@ -102,7 +103,7 @@ private async Task HandleResourceMetadataRequestAsync()
         Response.StatusCode = StatusCodes.Status200OK;
         Response.ContentType = "application/json";
 
-        var json = System.Text.Json.JsonSerializer.Serialize(
+        var json = JsonSerializer.Serialize(
             metadata, 
             McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(ProtectedResourceMetadata)));