diff --git a/tests/ModelContextProtocol.AspNetCore.Tests/MapMcpAuthorizationTests.cs b/tests/ModelContextProtocol.AspNetCore.Tests/MapMcpAuthorizationTests.cs
new file mode 100644
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+++ b/tests/ModelContextProtocol.AspNetCore.Tests/MapMcpAuthorizationTests.cs
@@ -0,0 +1,282 @@
+using Microsoft.AspNetCore.Authentication;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using ModelContextProtocol.AspNetCore.Authentication;
+using ModelContextProtocol.AspNetCore.Tests.Utils;
+using ModelContextProtocol.Authentication;
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Server;
+using ModelContextProtocol.Tests.Utils;
+using System.ComponentModel;
+using System.Net;
+using System.Net.Http.Json;
+using System.Net.ServerSentEvents;
+using System.Security.Claims;
+using System.Text;
+using System.Text.Encodings.Web;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+using System.Text.Json.Serialization.Metadata;
+
+namespace ModelContextProtocol.AspNetCore.Tests;
+
+/// <summary>
+/// End-to-end coverage for protecting the MCP endpoint itself with <c>RequireAuthorization()</c>.
+/// </summary>
+/// <remarks>
+/// <para>
+/// <see cref="AuthorizeAttributeTests"/> covers tool-level <c>[Authorize]</c>: the request reaches the MCP
+/// handler and the tool collection is filtered per user. This file covers the endpoint-level challenge
+/// instead, which has to happen before the request reaches the handler at all — for the initialize request,
+/// for follow-up requests inside an established session, and in either session mode.
+/// </para>
+/// <para>
+/// The last test covers the OAuth interaction: the protected-resource metadata document must stay reachable
+/// while the MCP endpoint itself requires credentials, and the challenge must point clients at it.
+/// </para>
+/// </remarks>
+[McpServerToolType]
+public class MapMcpAuthorizationTests(ITestOutputHelper outputHelper) : KestrelInMemoryTest(outputHelper), IAsyncDisposable
+{
+    private const string TestScheme = "TestScheme";
+    private const string UserHeaderName = "X-Test-User";
+    private const string McpEndpointUrl = "http://localhost:5000";
+    private const string AuthorizationServerUrl = "https://localhost:7029";
+
+    private WebApplication? _app;
+
+    [McpServerTool(Name = "echo")]
+    [Description("Echoes the supplied message back to the caller.")]
+    public static string Echo(string message) => $"Echo: {message}";
+
+    private async Task StartAsync(
+        HttpServerSessionMode sessionMode = HttpServerSessionMode.Stateful,
+        bool advertiseResourceMetadata = false,
+        string path = "")
+    {
+        Builder.Services.AddMcpServer()
+            .WithTools<MapMcpAuthorizationTests>()
+            .WithHttpTransport(options => options.SessionMode = sessionMode);
+
+        var authentication = Builder.Services.AddAuthentication(options =>
+        {
+            options.DefaultScheme = TestScheme;
+            options.DefaultAuthenticateScheme = TestScheme;
+
+            if (advertiseResourceMetadata)
+            {
+                // A real OAuth-protected server challenges with the MCP scheme so that the 401 advertises
+                // the protected-resource metadata document, while authentication itself is done per token.
+                options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;
+            }
+        });
+
+        authentication.AddScheme<AuthenticationSchemeOptions, HeaderUserAuthenticationHandler>(TestScheme, options => { });
+
+        if (advertiseResourceMetadata)
+        {
+            authentication.AddScheme<McpAuthenticationOptions, McpAuthenticationHandler>(
+                McpAuthenticationDefaults.AuthenticationScheme,
+                options => options.ResourceMetadata = new ProtectedResourceMetadata
+                {
+                    AuthorizationServers = { AuthorizationServerUrl },
+                    ScopesSupported = { "mcp:tools" },
+                });
+        }
+
+        Builder.Services.AddAuthorization();
+
+        _app = Builder.Build();
+
+        _app.MapMcp(path).RequireAuthorization();
+
+        await _app.StartAsync(TestContext.Current.CancellationToken);
+
+        HttpClient.DefaultRequestHeaders.Accept.Add(new("application/json"));
+        HttpClient.DefaultRequestHeaders.Accept.Add(new("text/event-stream"));
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        if (_app is not null)
+        {
+            await _app.DisposeAsync();
+        }
+
+        base.Dispose();
+    }
+
+    [Theory]
+    [InlineData(HttpServerSessionMode.Stateful)]
+    [InlineData(HttpServerSessionMode.StatefulForInitializeClients)]
+    [InlineData(HttpServerSessionMode.Stateless)]
+    public async Task Initialize_WithoutCredentials_IsChallenged(HttpServerSessionMode sessionMode)
+    {
+        await StartAsync(sessionMode);
+
+        using var response = await PostAsync(InitializeRequest);
+
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+    }
+
+    [Theory]
+    [InlineData(HttpServerSessionMode.Stateful)]
+    [InlineData(HttpServerSessionMode.StatefulForInitializeClients)]
+    [InlineData(HttpServerSessionMode.Stateless)]
+    public async Task Initialize_WithCredentials_Succeeds(HttpServerSessionMode sessionMode)
+    {
+        await StartAsync(sessionMode);
+
+        using var response = await PostAsync(InitializeRequest, user: "alice");
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        // Stateless mode keeps the endpoint free of server state, so only the session-based modes mint an id.
+        if (sessionMode is HttpServerSessionMode.Stateless)
+        {
+            Assert.False(response.Headers.Contains("mcp-session-id"));
+        }
+        else
+        {
+            Assert.False(string.IsNullOrEmpty(GetSessionId(response)));
+        }
+    }
+
+    [Fact]
+    public async Task StatefulSession_FollowUpRequests_RequireCredentials()
+    {
+        await StartAsync(HttpServerSessionMode.Stateful);
+
+        using var initializeResponse = await PostAsync(InitializeRequest, user: "alice");
+        var sessionId = GetSessionId(initializeResponse);
+        Assert.False(string.IsNullOrEmpty(sessionId));
+
+        using var authorizedResponse = await PostAsync(ListToolsRequest, user: "alice", sessionId: sessionId);
+        var result = AssertType<ListToolsResult>((await ReadSingleSseResponseAsync(authorizedResponse)).Result);
+        Assert.Contains(result.Tools, tool => tool.Name == "echo");
+
+        // The session id identifies the session; it must not authenticate the caller. Without credentials
+        // the authorization middleware has to reject the request before the MCP handler sees the session.
+        using var unauthenticatedResponse = await PostAsync(ListToolsRequest, sessionId: sessionId);
+        Assert.Equal(HttpStatusCode.Unauthorized, unauthenticatedResponse.StatusCode);
+    }
+
+    [Fact]
+    public async Task ResourceMetadata_RemainsReachable_WhileTheMcpEndpointIsChallenged()
+    {
+        // Mount the endpoint at /mcp, the shape a deployment behind an ingress typically uses: the metadata
+        // document then mirrors the resource path, and the challenge advertises that mirrored document.
+        await StartAsync(HttpServerSessionMode.Stateful, advertiseResourceMetadata: true, path: "/mcp");
+
+        // Discovery is what an unauthenticated client does first, so the metadata document has to be served
+        // without credentials even though every request to the MCP endpoint is challenged.
+        using var metadataResponse = await HttpClient.GetAsync(
+            "/.well-known/oauth-protected-resource/mcp", TestContext.Current.CancellationToken);
+
+        Assert.Equal(HttpStatusCode.OK, metadataResponse.StatusCode);
+
+        var metadata = await metadataResponse.Content.ReadFromJsonAsync<ProtectedResourceMetadata>(
+            McpJsonUtilities.DefaultOptions, TestContext.Current.CancellationToken);
+
+        Assert.NotNull(metadata);
+        Assert.Equal($"{McpEndpointUrl}/mcp", metadata.Resource);
+        Assert.Equal([AuthorizationServerUrl], metadata.AuthorizationServers);
+
+        // The challenge has to tell the client where the metadata document lives, otherwise it cannot
+        // discover the authorization server from the 401 alone.
+        using var challengedResponse = await PostAsync(InitializeRequest, path: "/mcp");
+
+        Assert.Equal(HttpStatusCode.Unauthorized, challengedResponse.StatusCode);
+        var challenge = Assert.Single(challengedResponse.Headers.WwwAuthenticate);
+        Assert.Equal("Bearer", challenge.Scheme);
+        Assert.Contains(
+            $"resource_metadata=\"{McpEndpointUrl}/.well-known/oauth-protected-resource/mcp\"",
+            challenge.Parameter);
+    }
+
+    private Task<HttpResponseMessage> PostAsync(string json, string? user = null, string? sessionId = null, string path = "")
+    {
+        var request = new HttpRequestMessage(HttpMethod.Post, path)
+        {
+            Content = new StringContent(json, Encoding.UTF8, "application/json"),
+        };
+
+        if (user is not null)
+        {
+            request.Headers.Add(UserHeaderName, user);
+        }
+
+        if (sessionId is not null)
+        {
+            request.Headers.Add("mcp-session-id", sessionId);
+        }
+
+        return HttpClient.SendAsync(request, TestContext.Current.CancellationToken);
+    }
+
+    private static string? GetSessionId(HttpResponseMessage response)
+        => response.Headers.TryGetValues("mcp-session-id", out var values) ? Assert.Single(values) : null;
+
+    private static async Task<JsonRpcResponse> ReadSingleSseResponseAsync(HttpResponseMessage response)
+    {
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        Assert.Equal("text/event-stream", response.Content.Headers.ContentType?.MediaType);
+
+        var responseStream = await response.Content.ReadAsStreamAsync(TestContext.Current.CancellationToken);
+        var payloads = new List<string>();
+
+        await foreach (var sseItem in SseParser.Create(responseStream).EnumerateAsync(TestContext.Current.CancellationToken))
+        {
+            Assert.Equal("message", sseItem.EventType);
+            payloads.Add(sseItem.Data);
+        }
+
+        var jsonRpcResponse = JsonSerializer.Deserialize(
+            Assert.Single(payloads),
+            (JsonTypeInfo<JsonRpcResponse>)McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(JsonRpcResponse)));
+
+        Assert.NotNull(jsonRpcResponse);
+        return jsonRpcResponse;
+    }
+
+    private static T AssertType<T>(JsonNode? jsonNode)
+    {
+        var value = JsonSerializer.Deserialize(
+            jsonNode, (JsonTypeInfo<T>)McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(T)));
+
+        Assert.NotNull(value);
+        return value;
+    }
+
+    private static string InitializeRequest => """
+        {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-11-25","capabilities":{},"clientInfo":{"name":"MapMcpAuthorizationTests","version":"1.0.0"}}}
+        """;
+
+    private static string ListToolsRequest => """
+        {"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}
+        """;
+
+    /// <summary>
+    /// Authenticates a caller from a header, so tests can assert both the challenged and the authorized path
+    /// without standing up a token issuer.
+    /// </summary>
+    private sealed class HeaderUserAuthenticationHandler(
+        IOptionsMonitor<AuthenticationSchemeOptions> options,
+        ILoggerFactory logger,
+        UrlEncoder encoder)
+        : AuthenticationHandler<AuthenticationSchemeOptions>(options, logger, encoder)
+    {
+        protected override Task<AuthenticateResult> HandleAuthenticateAsync()
+        {
+            if (!Request.Headers.TryGetValue(UserHeaderName, out var user) || string.IsNullOrEmpty(user))
+            {
+                return Task.FromResult(AuthenticateResult.NoResult());
+            }
+
+            var identity = new ClaimsIdentity([new Claim(ClaimTypes.Name, user.ToString())], TestScheme);
+            return Task.FromResult(AuthenticateResult.Success(new AuthenticationTicket(new ClaimsPrincipal(identity), TestScheme)));
+        }
+    }
+}