Reauthorize tools changed by call-tool filters

src/ModelContextProtocol.AspNetCore/AuthorizationFilterSetup.cs

@@ -20,6 +20,7 @@ internal sealed class AuthorizationFilterSetup(
     public void Configure(McpServerOptions options)
     {
         ConfigureListToolsFilter(options);
+        ConfigureOrdinaryCallToolFilter(options);
 
         ConfigureListResourcesFilter(options);
         ConfigureListResourceTemplatesFilter(options);
@@ -85,6 +86,22 @@ private static void CheckListToolsFilter(McpServerOptions options)
         });
     }
 
+    private void ConfigureOrdinaryCallToolFilter(McpServerOptions options)
+    {
+        options.Filters.Request.CallToolFilters.Add(next => async (context, cancellationToken) =>
+        {
+            var authResult = await GetAuthorizationResultAsync(context.User, context.MatchedPrimitive, context.Services, context);
+            if (!authResult.Succeeded)
+            {
+                throw new McpProtocolException("Access forbidden: This tool requires authorization.", McpErrorCode.InvalidRequest);
+            }
+
+            context.Items[AuthorizationFilterInvokedKey] = true;
+
+            return await next(context, cancellationToken);
+        });
+    }
+
     private void ConfigureCallToolFilter(McpServerOptions options)
     {
 #pragma warning disable MCPEXP002 // Authorization must run in the alternate-result pipeline before task dispatch.

src/ModelContextProtocol.AspNetCore/HttpMcpServerBuilderExtensions.cs

@@ -58,6 +58,7 @@ public static IMcpServerBuilder WithHttpTransport(this IMcpServerBuilder builder
     /// authorization attributes such as <see cref="AuthorizeAttribute"/>
     /// and <see cref="AllowAnonymousAttribute"/>. Tool authorization runs in the alternate-result pipeline before
     /// the Tasks extension dispatches background execution, so an unauthorized tool call does not create a task.
+    /// Call this method again after any call-tool filter that changes the matched tool to authorize the replacement.
     /// </remarks>
     public static IMcpServerBuilder AddAuthorizationFilters(this IMcpServerBuilder builder)
     {

src/ModelContextProtocol.Extensions.Tasks/Server/McpTasksBuilderExtensions.cs

@@ -23,7 +23,6 @@ public static class McpTasksBuilderExtensions
     /// Tasks are implemented as an alternate-result call-tool filter. Alternate-result filters registered before
     /// the Tasks filter run before task creation. Filters registered after it, along with all ordinary call-tool
     /// filters, run in the background before the tool.
-    /// Register Tasks before configuring ordinary call-tool filters.
     /// </remarks>
     /// <param name="builder">The server builder.</param>
     /// <param name="store">The task store.</param>
@@ -79,13 +78,6 @@ public void Configure(McpServerOptions options)
             options.RequestHandlers.Add(new McpServerRequestHandler { Method = TasksProtocol.MethodTasksUpdate, Handler = HandleUpdateTask });
             options.RequestHandlers.Add(new McpServerRequestHandler { Method = TasksProtocol.MethodTasksCancel, Handler = HandleCancelTask });
 
-            if (options.Filters.Request.CallToolFilters.Count > 0)
-            {
-                throw new InvalidOperationException(
-                    $"{nameof(WithTasks)} must be configured before ordinary call-tool filters because " +
-                    "the Tasks filter must execute outside the ordinary call-tool pipeline.");
-            }
-
             // Use a filter rather than a handler so it wraps around Core's tool dispatch.
             // This ensures it intercepts tool calls BEFORE the tool is invoked, allowing
             // it to spawn background execution and return the task alternate immediately.

tests/ModelContextProtocol.AspNetCore.Tests/AuthorizeAttributeTests.cs

@@ -93,6 +93,41 @@ public async Task Authorize_Tool_AllowsAuthenticatedUser()
         Assert.Equal("Authorized: test", content.Text);
     }
 
+    [Fact]
+    public async Task Authorize_Tool_ReauthorizesPrimitiveChangedByInterveningFilter()
+    {
+        await using var app = await StartServerWithAuth(builder =>
+        {
+            builder.WithTools<AuthorizationTestTools>();
+            builder.Services.Configure<McpServerOptions>(options =>
+            {
+                if (options.ToolCollection is null ||
+                    !options.ToolCollection.TryGetPrimitive("authorized_tool", out var authorizedTool))
+                {
+                    throw new InvalidOperationException("The replacement tool was not registered.");
+                }
+
+                options.Filters.Request.CallToolFilters.Add(next => async (context, cancellationToken) =>
+                {
+                    context.MatchedPrimitive = authorizedTool;
+                    return await next(context, cancellationToken);
+                });
+            });
+            builder.AddAuthorizationFilters();
+        });
+
+        var client = await ConnectAsync();
+
+        var exception = await Assert.ThrowsAsync<McpProtocolException>(async () =>
+            await client.CallToolAsync(
+                "anonymous_tool",
+                new Dictionary<string, object?> { ["message"] = "test" },
+                cancellationToken: TestContext.Current.CancellationToken));
+
+        Assert.Equal("Request failed (remote): Access forbidden: This tool requires authorization.", exception.Message);
+        Assert.Equal(McpErrorCode.InvalidRequest, exception.ErrorCode);
+    }
+
     [Fact]
     public async Task AuthorizeWithRoles_Tool_RequiresAdminRole()
     {

tests/ModelContextProtocol.AspNetCore.Tests/HttpTaskIntegrationTests.cs

@@ -1,7 +1,6 @@
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.Options;
 using ModelContextProtocol.AspNetCore.Tests.Utils;
 using ModelContextProtocol.Client;
 using ModelContextProtocol.Extensions.Tasks;
@@ -44,23 +43,41 @@ public async Task WithTasks_CanCallToolOverHttp()
     }
 
     [Fact]
-    public async Task WithTasks_AfterOrdinaryFilter_ThrowsActionableError()
+    public async Task WithTasks_AfterOrdinaryFilter_RunsFilter()
     {
+        var filterInvocationCount = 0;
         Builder.Services
             .AddMcpServer(options =>
             {
-                options.Filters.Request.CallToolFilters.Add(next => next);
+                options.Filters.Request.CallToolFilters.Add(next => async (context, cancellationToken) =>
+                {
+                    Interlocked.Increment(ref filterInvocationCount);
+                    return await next(context, cancellationToken);
+                });
             })
             .WithHttpTransport()
             .WithTasks(new InMemoryMcpTaskStore { DefaultPollIntervalMs = 10 })
             .WithTools<TestTools>();
 
         await using var app = Builder.Build();
+        app.MapMcp();
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        await using var transport = new HttpClientTransport(
+            new HttpClientTransportOptions { Endpoint = new("http://localhost:5000") },
+            HttpClient,
+            LoggerFactory);
+        await using var client = await McpClient.CreateAsync(
+            transport,
+            loggerFactory: LoggerFactory,
+            cancellationToken: TestContext.Current.CancellationToken);
 
-        var exception = Assert.Throws<InvalidOperationException>(
-            () => app.Services.GetRequiredService<IOptions<McpServerOptions>>().Value);
-        Assert.Contains(nameof(McpTasksBuilderExtensions.WithTasks), exception.Message);
-        Assert.Contains("before ordinary call-tool filters", exception.Message);
+        var result = await client.CallToolWithPollingAsync(
+            new CallToolRequestParams { Name = "test" },
+            cancellationToken: TestContext.Current.CancellationToken);
+
+        Assert.Equal("Hello World!", Assert.IsType<TextContentBlock>(Assert.Single(result.Content)).Text);
+        Assert.Equal(1, filterInvocationCount);
     }
 
     [Theory]
@@ -165,6 +182,54 @@ public async Task WithTasks_UnauthorizedTool_DoesNotCreateTask(bool registerTask
             Times.Never);
     }
 
+    [Fact]
+    public async Task WithTasks_ReauthorizesToolChangedByOrdinaryFilter()
+    {
+        var serverBuilder = Builder.Services
+            .AddMcpServer()
+            .WithHttpTransport()
+            .WithTasks(new InMemoryMcpTaskStore { DefaultPollIntervalMs = 10 })
+            .WithTools<TestTools>()
+            .AddAuthorizationFilters();
+
+        serverBuilder.Services.Configure<McpServerOptions>(options =>
+        {
+            if (options.ToolCollection is null ||
+                !options.ToolCollection.TryGetPrimitive("authorized-test", out var authorizedTool))
+            {
+                throw new InvalidOperationException("The replacement tool was not registered.");
+            }
+
+            options.Filters.Request.CallToolFilters.Add(next => async (context, cancellationToken) =>
+            {
+                context.MatchedPrimitive = authorizedTool;
+                return await next(context, cancellationToken);
+            });
+        });
+        serverBuilder.AddAuthorizationFilters();
+        Builder.Services.AddAuthorization();
+
+        await using var app = Builder.Build();
+        app.MapMcp();
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        await using var transport = new HttpClientTransport(
+            new HttpClientTransportOptions { Endpoint = new("http://localhost:5000") },
+            HttpClient,
+            LoggerFactory);
+        await using var client = await McpClient.CreateAsync(
+            transport,
+            loggerFactory: LoggerFactory,
+            cancellationToken: TestContext.Current.CancellationToken);
+
+        var exception = await Assert.ThrowsAsync<McpException>(() =>
+            client.CallToolWithPollingAsync(
+                new CallToolRequestParams { Name = "test" },
+                cancellationToken: TestContext.Current.CancellationToken).AsTask());
+
+        Assert.Contains("Access forbidden: This tool requires authorization.", exception.Message);
+    }
+
     [McpServerToolType]
     private sealed class TestTools
     {