fix: Prevent crash when Options.ResourceMetadata is null but handled by event (#603)

src/ModelContextProtocol.AspNetCore/Authentication/McpAuthenticationHandler.cs

@@ -43,8 +43,7 @@ public class McpAuthenticationHandler : AuthenticationHandler<McpAuthenticationO
             return false;
         }
 
-        var cancellationToken = Request.HttpContext.RequestAborted;
+        await HandleResourceMetadataRequestAsync();
-        await HandleResourceMetadataRequestAsync(cancellationToken);
         return true;
     }
 
@@ -82,8 +81,7 @@ public class McpAuthenticationHandler : AuthenticationHandler<McpAuthenticationO
     /// <summary>
     /// Handles the resource metadata request.
     /// </summary>
-    /// <param name="cancellationToken">A token to cancel the operation.</param>
+    private async Task HandleResourceMetadataRequestAsync()
-    private async Task HandleResourceMetadataRequestAsync(CancellationToken cancellationToken = default)
     {
         var resourceMetadata = Options.ResourceMetadata;
 
@@ -95,12 +93,14 @@ public class McpAuthenticationHandler : AuthenticationHandler<McpAuthenticationO
             };
 
             await Options.Events.OnResourceMetadataRequest(context);
+            resourceMetadata = context.ResourceMetadata;
         }
 
-
         if (resourceMetadata == null)
         {
-            throw new InvalidOperationException("ResourceMetadata has not been configured. Please set McpAuthenticationOptions.ResourceMetadata.");
+            throw new InvalidOperationException(
+                "ResourceMetadata has not been configured. Please set McpAuthenticationOptions.ResourceMetadata or ensure context.ResourceMetadata is set inside McpAuthenticationOptions.Events.OnResourceMetadataRequest."
+            );
         }
 
         await Results.Json(resourceMetadata, McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(ProtectedResourceMetadata))).ExecuteAsync(Context);

tests/ModelContextProtocol.AspNetCore.Tests/AuthEventTests.cs

@@ -0,0 +1,310 @@
+using System.Net;
+using System.Net.Http.Json;
+using System.Text.Json;
+using Microsoft.AspNetCore.Authentication.JwtBearer;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.WebUtilities;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.IdentityModel.Tokens;
+using ModelContextProtocol.AspNetCore.Authentication;
+using ModelContextProtocol.AspNetCore.Tests.Utils;
+using ModelContextProtocol.Authentication;
+using ModelContextProtocol.Client;
+
+namespace ModelContextProtocol.AspNetCore.Tests;
+
+/// <summary>
+/// Tests for MCP authentication when resource metadata is provided via events rather than static configuration.
+/// </summary>
+public class AuthEventTests : KestrelInMemoryTest, IAsyncDisposable
+{
+    private const string McpServerUrl = "http://localhost:5000";
+    private const string OAuthServerUrl = "https://localhost:7029";
+
+    private readonly CancellationTokenSource _testCts = new();
+    private readonly TestOAuthServer.Program _testOAuthServer;
+    private readonly Task _testOAuthRunTask;
+
+    public AuthEventTests(ITestOutputHelper outputHelper)
+        : base(outputHelper)
+    {
+        // Let the HandleAuthorizationUrlAsync take a look at the Location header
+        SocketsHttpHandler.AllowAutoRedirect = false;
+        // The dev cert may not be installed on the CI, but AddJwtBearer requires an HTTPS backchannel by default.
+        // The easiest workaround is to disable cert validation for testing purposes.
+        SocketsHttpHandler.SslOptions.RemoteCertificateValidationCallback = (_, _, _, _) => true;
+
+        _testOAuthServer = new TestOAuthServer.Program(
+            XunitLoggerProvider,
+            KestrelInMemoryTransport
+        );
+        _testOAuthRunTask = _testOAuthServer.RunServerAsync(cancellationToken: _testCts.Token);
+
+        Builder
+            .Services.AddAuthentication(options =>
+            {
+                options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;
+                options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
+            })
+            .AddJwtBearer(options =>
+            {
+                options.Backchannel = HttpClient;
+                options.Authority = OAuthServerUrl;
+                options.TokenValidationParameters = new TokenValidationParameters
+                {
+                    ValidateIssuer = true,
+                    ValidateAudience = true,
+                    ValidateLifetime = true,
+                    ValidateIssuerSigningKey = true,
+                    ValidAudience = McpServerUrl,
+                    ValidIssuer = OAuthServerUrl,
+                    NameClaimType = "name",
+                    RoleClaimType = "roles",
+                };
+            })
+            .AddMcp(options =>
+            {
+                // Note: ResourceMetadata is NOT set here - it will be provided via events
+                options.Events.OnResourceMetadataRequest = async context =>
+                {
+                    // Dynamically provide the resource metadata
+                    context.ResourceMetadata = new ProtectedResourceMetadata
+                    {
+                        Resource = new Uri(McpServerUrl),
+                        AuthorizationServers = { new Uri(OAuthServerUrl) },
+                        ScopesSupported = ["mcp:tools"],
+                    };
+                    await Task.CompletedTask;
+                };
+            });
+
+        Builder.Services.AddAuthorization();
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        _testCts.Cancel();
+        try
+        {
+            await _testOAuthRunTask;
+        }
+        catch (OperationCanceledException) { }
+        finally
+        {
+            _testCts.Dispose();
+        }
+    }
+
+    [Fact]
+    public async Task CanAuthenticate_WithResourceMetadataFromEvent()
+    {
+        Builder.Services.AddMcpServer().WithHttpTransport();
+
+        await using var app = Builder.Build();
+
+        app.MapMcp().RequireAuthorization();
+
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        await using var transport = new SseClientTransport(
+            new()
+            {
+                Endpoint = new(McpServerUrl),
+                OAuth = new()
+                {
+                    ClientId = "demo-client",
+                    ClientSecret = "demo-secret",
+                    RedirectUri = new Uri("http://localhost:1179/callback"),
+                    AuthorizationRedirectDelegate = HandleAuthorizationUrlAsync,
+                },
+            },
+            HttpClient,
+            LoggerFactory
+        );
+
+        await using var client = await McpClientFactory.CreateAsync(
+            transport,
+            loggerFactory: LoggerFactory,
+            cancellationToken: TestContext.Current.CancellationToken
+        );
+    }
+
+    [Fact]
+    public async Task CanAuthenticate_WithDynamicClientRegistration_FromEvent()
+    {
+        Builder.Services.AddMcpServer().WithHttpTransport();
+
+        await using var app = Builder.Build();
+
+        app.MapMcp().RequireAuthorization();
+
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        await using var transport = new SseClientTransport(
+            new()
+            {
+                Endpoint = new(McpServerUrl),
+                OAuth = new ClientOAuthOptions()
+                {
+                    RedirectUri = new Uri("http://localhost:1179/callback"),
+                    AuthorizationRedirectDelegate = HandleAuthorizationUrlAsync,
+                    ClientName = "Test MCP Client",
+                    ClientUri = new Uri("https://example.com"),
+                    Scopes = ["mcp:tools"],
+                },
+            },
+            HttpClient,
+            LoggerFactory
+        );
+
+        await using var client = await McpClientFactory.CreateAsync(
+            transport,
+            loggerFactory: LoggerFactory,
+            cancellationToken: TestContext.Current.CancellationToken
+        );
+    }
+
+    [Fact]
+    public async Task ResourceMetadataEndpoint_ReturnsCorrectMetadata_FromEvent()
+    {
+        Builder.Services.AddMcpServer().WithHttpTransport();
+
+        await using var app = Builder.Build();
+
+        app.MapMcp().RequireAuthorization();
+
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        // Make a direct request to the resource metadata endpoint
+        using var response = await HttpClient.GetAsync(
+            "/.well-known/oauth-protected-resource",
+            TestContext.Current.CancellationToken
+        );
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var metadata = await response.Content.ReadFromJsonAsync<ProtectedResourceMetadata>(
+            McpJsonUtilities.DefaultOptions,
+            TestContext.Current.CancellationToken
+        );
+
+        Assert.NotNull(metadata);
+        Assert.Equal(new Uri(McpServerUrl), metadata.Resource);
+        Assert.Contains(new Uri(OAuthServerUrl), metadata.AuthorizationServers);
+        Assert.Contains("mcp:tools", metadata.ScopesSupported);
+    }
+
+    [Fact]
+    public async Task ResourceMetadataEndpoint_CanModifyExistingMetadata_InEvent()
+    {
+        Builder.Services.AddMcpServer().WithHttpTransport();
+
+        // Override the configuration to test modification of existing metadata
+        Builder.Services.Configure<McpAuthenticationOptions>(
+            McpAuthenticationDefaults.AuthenticationScheme,
+            options =>
+            {
+                // Set initial metadata
+                options.ResourceMetadata = new ProtectedResourceMetadata
+                {
+                    Resource = new Uri(McpServerUrl),
+                    AuthorizationServers = { new Uri(OAuthServerUrl) },
+                    ScopesSupported = ["mcp:basic"],
+                };
+
+                // Override the event to modify the metadata
+                options.Events.OnResourceMetadataRequest = async context =>
+                {
+                    // Start with the existing metadata and modify it
+                    if (context.ResourceMetadata != null)
+                    {
+                        context.ResourceMetadata.ScopesSupported.Add("mcp:tools");
+                        context.ResourceMetadata.ResourceName = "Dynamic Test Resource";
+                    }
+                    await Task.CompletedTask;
+                };
+            }
+        );
+
+        await using var app = Builder.Build();
+
+        app.MapMcp().RequireAuthorization();
+
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        // Make a direct request to the resource metadata endpoint
+        using var response = await HttpClient.GetAsync(
+            "/.well-known/oauth-protected-resource",
+            TestContext.Current.CancellationToken
+        );
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var metadata = await response.Content.ReadFromJsonAsync<ProtectedResourceMetadata>(
+            McpJsonUtilities.DefaultOptions,
+            TestContext.Current.CancellationToken
+        );
+
+        Assert.NotNull(metadata);
+        Assert.Equal(new Uri(McpServerUrl), metadata.Resource);
+        Assert.Contains(new Uri(OAuthServerUrl), metadata.AuthorizationServers);
+        Assert.Contains("mcp:basic", metadata.ScopesSupported);
+        Assert.Contains("mcp:tools", metadata.ScopesSupported);
+        Assert.Equal("Dynamic Test Resource", metadata.ResourceName);
+    }
+
+    [Fact]
+    public async Task ResourceMetadataEndpoint_ThrowsException_WhenNoMetadataProvided()
+    {
+        Builder.Services.AddMcpServer().WithHttpTransport();
+
+        // Override the configuration to test the error case where no metadata is provided
+        Builder.Services.Configure<McpAuthenticationOptions>(
+            McpAuthenticationDefaults.AuthenticationScheme,
+            options =>
+            {
+                // Don't set ResourceMetadata and provide an event that doesn't set it either
+                options.ResourceMetadata = null;
+                options.Events.OnResourceMetadataRequest = async context =>
+                {
+                    // Intentionally don't set context.ResourceMetadata to test error handling
+                    await Task.CompletedTask;
+                };
+            }
+        );
+
+        await using var app = Builder.Build();
+
+        app.MapMcp().RequireAuthorization();
+
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        // Make a direct request to the resource metadata endpoint - this should fail
+        using var response = await HttpClient.GetAsync(
+            "/.well-known/oauth-protected-resource",
+            TestContext.Current.CancellationToken
+        );
+
+        // The request should fail with an internal server error due to the InvalidOperationException
+        Assert.Equal(HttpStatusCode.InternalServerError, response.StatusCode);
+    }
+
+    private async Task<string?> HandleAuthorizationUrlAsync(
+        Uri authorizationUri,
+        Uri redirectUri,
+        CancellationToken cancellationToken
+    )
+    {
+        using var redirectResponse = await HttpClient.GetAsync(authorizationUri, cancellationToken);
+        Assert.Equal(HttpStatusCode.Redirect, redirectResponse.StatusCode);
+        var location = redirectResponse.Headers.Location;
+
+        if (location is not null && !string.IsNullOrEmpty(location.Query))
+        {
+            var queryParams = QueryHelpers.ParseQuery(location.Query);
+            return queryParams["code"];
+        }
+
+        return null;
+    }
+}