Add middleware and authz support for server-side handlers (#733)

Author: halter73

docs/concepts/filters.md

@@ -0,0 +1,317 @@
+---
+title: Filters
+author: halter73
+description: MCP Server Handler Filters
+uid: filters
+---
+
+# MCP Server Handler Filters
+
+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
+
+The following filter methods are available:
+
+- `AddListResourceTemplatesFilter` - Filter for list resource templates handlers
+- `AddListToolsFilter` - Filter for list tools handlers
+- `AddCallToolFilter` - Filter for call tool handlers
+- `AddListPromptsFilter` - Filter for list prompts handlers
+- `AddGetPromptFilter` - Filter for get prompt handlers
+- `AddListResourcesFilter` - Filter for list resources handlers
+- `AddReadResourceFilter` - Filter for read resource handlers
+- `AddCompleteFilter` - Filter for completion handlers
+- `AddSubscribeToResourcesFilter` - Filter for resource subscription handlers
+- `AddUnsubscribeFromResourcesFilter` - Filter for resource unsubscription handlers
+- `AddSetLoggingLevelFilter` - Filter for logging level handlers
+
+## Usage
+
+Filters are functions that take a handler and return a new handler, allowing you to wrap the original handler with additional functionality:
+
+```csharp
+services.AddMcpServer()
+    .WithListToolsHandler(async (context, cancellationToken) =>
+    {
+        // Your base handler logic
+        return new ListToolsResult { Tools = GetTools() };
+    })
+    .AddListToolsFilter(next => async (context, cancellationToken) =>
+    {
+        var logger = context.Services?.GetService<ILogger<Program>>();
+
+        // Pre-processing logic
+        logger?.LogInformation("Before handler execution");
+
+        var result = await next(context, cancellationToken);
+
+        // Post-processing logic
+        logger?.LogInformation("After handler execution");
+        return result;
+    });
+```
+
+## Filter Execution Order
+
+```csharp
+services.AddMcpServer()
+    .WithListToolsHandler(baseHandler)
+    .AddListToolsFilter(filter1)  // Executes first (outermost)
+    .AddListToolsFilter(filter2)  // Executes second
+    .AddListToolsFilter(filter3); // Executes third (closest to handler)
+```
+
+Execution flow: `filter1 -> filter2 -> filter3 -> baseHandler -> filter3 -> filter2 -> filter1`
+
+## Common Use Cases
+
+### Logging
+```csharp
+.AddListToolsFilter(next => async (context, cancellationToken) =>
+{
+    var logger = context.Services?.GetService<ILogger<Program>>();
+
+    logger?.LogInformation($"Processing request from {context.Meta.ProgressToken}");
+    var result = await next(context, cancellationToken);
+    logger?.LogInformation($"Returning {result.Tools?.Count ?? 0} tools");
+    return result;
+});
+```
+
+### Error Handling
+```csharp
+.AddCallToolFilter(next => async (context, cancellationToken) =>
+{
+    try
+    {
+        return await next(context, cancellationToken);
+    }
+    catch (Exception ex)
+    {
+        return new CallToolResult
+        {
+            Content = new[] { new TextContent { Type = "text", Text = $"Error: {ex.Message}" } },
+            IsError = true
+        };
+    }
+});
+```
+
+### Performance Monitoring
+```csharp
+.AddListToolsFilter(next => async (context, cancellationToken) =>
+{
+    var logger = context.Services?.GetService<ILogger<Program>>();
+
+    var stopwatch = Stopwatch.StartNew();
+    var result = await next(context, cancellationToken);
+    stopwatch.Stop();
+    logger?.LogInformation($"Handler took {stopwatch.ElapsedMilliseconds}ms");
+    return result;
+});
+```
+
+### Caching
+```csharp
+.AddListResourcesFilter(next => async (context, cancellationToken) =>
+{
+    var cache = context.Services!.GetRequiredService<IMemoryCache>();
+
+    var cacheKey = $"resources:{context.Params.Cursor}";
+    if (cache.TryGetValue(cacheKey, out var cached))
+    {
+        return (ListResourcesResult)cached;
+    }
+
+    var result = await next(context, cancellationToken);
+    cache.Set(cacheKey, result, TimeSpan.FromMinutes(5));
+    return result;
+});
+```
+
+## Built-in Authorization Filters
+
+When using the ASP.NET Core integration (`ModelContextProtocol.AspNetCore`), you can add authorization filters to support `[Authorize]` and `[AllowAnonymous]` attributes on MCP server tools, prompts, and resources by calling `AddAuthorizationFilters()` on your MCP server builder.
+
+### Enabling Authorization Filters
+
+To enable authorization support, call `AddAuthorizationFilters()` when configuring your MCP server:
+
+```csharp
+services.AddMcpServer()
+    .WithHttpTransport()
+    .AddAuthorizationFilters() // Enable authorization filter support
+    .WithTools<WeatherTools>();
+```
+
+**Important**: You should always call `AddAuthorizationFilters()` when using ASP.NET Core integration if you want to use authorization attributes like `[Authorize]` on your MCP server tools, prompts, or resources.
+
+### Authorization Attributes Support
+
+The MCP server automatically respects the following authorization attributes:
+
+- **`[Authorize]`** - Requires authentication for access
+- **`[Authorize(Roles = "RoleName")]`** - Requires specific roles
+- **`[Authorize(Policy = "PolicyName")]`** - Requires specific authorization policies
+- **`[AllowAnonymous]`** - Explicitly allows anonymous access (overrides `[Authorize]`)
+
+### Tool Authorization
+
+Tools can be decorated with authorization attributes to control access:
+
+```csharp
+[McpServerToolType]
+public class WeatherTools
+{
+    [McpServerTool, Description("Gets public weather data")]
+    public static string GetWeather(string location)
+    {
+        return $"Weather for {location}: Sunny, 25°C";
+    }
+
+    [McpServerTool, Description("Gets detailed weather forecast")]
+    [Authorize] // Requires authentication
+    public static string GetDetailedForecast(string location)
+    {
+        return $"Detailed forecast for {location}: ...";
+    }
+
+    [McpServerTool, Description("Manages weather alerts")]
+    [Authorize(Roles = "Admin")] // Requires Admin role
+    public static string ManageWeatherAlerts(string alertType)
+    {
+        return $"Managing alert: {alertType}";
+    }
+}
+```
+
+### Class-Level Authorization
+
+You can apply authorization at the class level, which affects all tools in the class:
+
+```csharp
+[McpServerToolType]
+[Authorize] // All tools require authentication
+public class RestrictedTools
+{
+    [McpServerTool, Description("Restricted tool accessible to authenticated users")]
+    public static string RestrictedOperation()
+    {
+        return "Restricted operation completed";
+    }
+
+    [McpServerTool, Description("Public tool accessible to anonymous users")]
+    [AllowAnonymous] // Overrides class-level [Authorize]
+    public static string PublicOperation()
+    {
+        return "Public operation completed";
+    }
+}
+```
+
+### How Authorization Filters Work
+
+The authorization filters work differently for list operations versus individual operations:
+
+#### List Operations (ListTools, ListPrompts, ListResources)
+For list operations, the filters automatically remove unauthorized items from the results. Users only see tools, prompts, or resources they have permission to access.
+
+#### Individual Operations (CallTool, GetPrompt, ReadResource)
+For individual operations, the filters throw an `McpException` with "Access forbidden" message. These get turned into JSON-RPC errors if uncaught by middleware.
+
+### Filter Execution Order and Authorization
+
+Authorization filters are applied automatically when you call `AddAuthorizationFilters()`. These filters run at a specific point in the filter pipeline, which means:
+
+**Filters added before authorization filters** can see:
+- Unauthorized requests for operations before they are rejected by the authorization filters
+- Complete listings for unauthorized primitives before they are filtered out by the authorization filters
+
+**Filters added after authorization filters** will only see:
+- Authorized requests that passed authorization checks
+- Filtered listings containing only authorized primitives
+
+This allows you to implement logging, metrics, or other cross-cutting concerns that need to see all requests, while still maintaining proper authorization:
+
+```csharp
+services.AddMcpServer()
+    .WithHttpTransport()
+    .AddListToolsFilter(next => async (context, cancellationToken) =>
+    {
+        var logger = context.Services?.GetService<ILogger<Program>>();
+
+        // This filter runs BEFORE authorization - sees all tools
+        logger?.LogInformation("Request for tools list - will see all tools");
+        var result = await next(context, cancellationToken);
+        logger?.LogInformation($"Returning {result.Tools?.Count ?? 0} tools after authorization");
+        return result;
+    })
+    .AddAuthorizationFilters() // Authorization filtering happens here
+    .AddListToolsFilter(next => async (context, cancellationToken) =>
+    {
+        var logger = context.Services?.GetService<ILogger<Program>>();
+
+        // This filter runs AFTER authorization - only sees authorized tools
+        var result = await next(context, cancellationToken);
+        logger?.LogInformation($"Post-auth filter sees {result.Tools?.Count ?? 0} authorized tools");
+        return result;
+    })
+    .WithTools<WeatherTools>();
+```
+
+### Setup Requirements
+
+To use authorization features, you must configure authentication and authorization in your ASP.NET Core application and call `AddAuthorizationFilters()`:
+
+```csharp
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddAuthentication("Bearer")
+    .AddJwtBearer(options => { /* JWT configuration */ })
+    .AddMcp(options => { /* Resource metadata configuration */ });
+builder.Services.AddAuthorization();
+
+builder.Services.AddMcpServer()
+    .WithHttpTransport()
+    .AddAuthorizationFilters() // Required for authorization support
+    .WithTools<WeatherTools>()
+    .AddCallToolFilter(next => async (context, cancellationToken) =>
+    {
+        // Custom call tool logic
+        return await next(context, cancellationToken);
+    });
+
+var app = builder.Build();
+
+app.MapMcp();
+app.Run();
+```
+
+### Custom Authorization Filters
+
+You can also create custom authorization filters using the filter methods:
+
+```csharp
+.AddCallToolFilter(next => async (context, cancellationToken) =>
+{
+    // Custom authorization logic
+    if (context.User?.Identity?.IsAuthenticated != true)
+    {
+        return new CallToolResult
+        {
+            Content = [new TextContent { Text = "Custom: Authentication required" }],
+            IsError = true
+        };
+    }
+
+    return await next(context, cancellationToken);
+});
+```
+
+### RequestContext
+
+Within filters, you have access to:
+
+- `context.User` - The current user's `ClaimsPrincipal`
+- `context.Services` - The request's service provider for resolving authorization services
+- `context.MatchedPrimitive` - The matched tool/prompt/resource with its metadata including authorization attributes via `context.MatchedPrimitive.Metadata`

docs/concepts/toc.yml

@@ -13,3 +13,7 @@ items:
   items:
   - name: Logging
     uid: logging
+- name: Server Features
+  items:
+  - name: Filters
+    uid: filters

samples/AspNetCoreMcpServer/Properties/launchSettings.json

@@ -7,7 +7,7 @@
       "applicationUrl": "http://localhost:3001",
       "environmentVariables": {
         "ASPNETCORE_ENVIRONMENT": "Development",
-        "OTEL_SERVICE_NAME": "aspnetcore-mcp-server",
+        "OTEL_SERVICE_NAME": "aspnetcore-mcp-server"
       }
     },
     "https": {
@@ -16,7 +16,7 @@
       "applicationUrl": "https://localhost:7133;http://localhost:3001",
       "environmentVariables": {
         "ASPNETCORE_ENVIRONMENT": "Development",
-        "OTEL_SERVICE_NAME": "aspnetcore-mcp-server",
+        "OTEL_SERVICE_NAME": "aspnetcore-mcp-server"
       }
     }
   }