Fix failing Windows build

- filters.md cleanup

Author: halter73

docs/concepts/filters.md

@@ -7,10 +7,6 @@ uid: filters
 
 # MCP Server Handler Filters
 
-This document describes the filter functionality in the MCP Server, which allows you to add middleware-style filters to handler pipelines.
-
-## Overview
-
 For each handler type in the MCP Server, there are corresponding `AddXXXFilter` methods in `McpServerBuilderExtensions.cs` that allow you to add filters to the handler pipeline. The filters are stored in `McpServerOptions.Filters` and applied during server configuration.
 
 ## Available Filter Methods
@@ -173,12 +169,12 @@ You can apply authorization at the class level, which affects all tools in the c
 ```csharp
 [McpServerToolType]
 [Authorize] // All tools require authentication
-public class AdminTools
+public class RestrictedTools
 {
-    [McpServerTool, Description("Admin-only tool")]
-    public static string AdminOperation()
+    [McpServerTool, Description("Restricted tool accessible to authenticated users")]
+    public static string RestrictedOperation()
     {
-        return "Admin operation completed";
+        return "Restricted operation completed";
     }
 
     [McpServerTool, Description("Public tool accessible to anonymous users")]
@@ -211,23 +207,22 @@ To use authorization features, you must configure authentication and authorizati
 ```csharp
 var builder = WebApplication.CreateBuilder(args);
 
-// Add authentication
 builder.Services.AddAuthentication("Bearer")
-    .AddJwtBearer("Bearer", options => { /* JWT configuration */ });
-
-// Add authorization (required for [Authorize] attributes to work)
+    .AddJwtBearer(options => { /* JWT configuration */ })
+    .AddMcp(options => { /* Resource metadata configuration */ });
 builder.Services.AddAuthorization();
 
-// Add MCP server
 builder.Services.AddMcpServer()
-    .WithTools<WeatherTools>();
+    .WithHttpTransport()
+    .WithTools<WeatherTools>()
+    .AddCallToolFilter(next => async (context, cancellationToken) =>
+    {
+        // Custom call tool logic
+        return await next(context, cancellationToken);
+    });
 
 var app = builder.Build();
 
-// Use authentication and authorization middleware
-app.UseAuthentication();
-app.UseAuthorization();
-
 app.MapMcp();
 app.Run();
 ```

src/ModelContextProtocol.AspNetCore/StreamableHttpHandler.cs

@@ -279,9 +279,11 @@ internal static string MakeNewSessionId()
         // Implementation for reading a JSON-RPC message from the request body
         var message = await context.Request.ReadFromJsonAsync(s_messageTypeInfo, context.RequestAborted);
 
-        if (context.User?.Identity?.IsAuthenticated ?? false)
+        if (context.User?.Identity?.IsAuthenticated ?? false && message is not null)
         {
-            message?.Context = new()
+            // We get weird CS0131 errors only on the Windows build GitHub Action if we use "message?.Context = ..."
+            // https://productionresultssa0.blob.core.windows.net/actions-results/f2218319-0fdd-473b-891d-06e5a4a0f826/workflow-job-run-98901492-cf7c-5406-85d9-0f7057e0516f/logs/job/job-logs.txt?rsct=text%2Fplain&se=2025-08-26T16%3A06%3A31Z&sig=RvEQo6DgrpDUW9mnbgDvf6FVDAAoHKzk9rsDdcPxOhw%3D&ske=2025-08-27T03%3A39%3A43Z&skoid=ca7593d4-ee42-46cd-af88-8b886a2f84eb&sks=b&skt=2025-08-26T15%3A39%3A43Z&sktid=398a6654-997b-47e9-b12b-9515b896b4de&skv=2025-05-05&sp=r&spr=https&sr=b&st=2025-08-26T15%3A56%3A26Z&sv=2025-05-05
+            message!.Context = new()
             {
                 User = context.User,
             };