.NET: DevUI: add configurable access controls for the DevUI HTTP surface (#5739)

* .NET: DevUI: add configurable access controls for the DevUI HTTP surface

* .NET: DevUI: address review and fix dotnet format

- Restore parameterless AddDevUI overloads for binary compatibility on
  IServiceCollection and IHostApplicationBuilder.
- Keep /meta outside the auth-filtered group so the frontend can discover
  whether a bearer token is required before prompting for one. Surface the
  actual requirement via MetaResponse.auth_required.
- Invoke DevUIOptions.ConfigureEndpoints before mapping protected endpoints
  so RouteGroupBuilder conventions (RequireAuthorization, rate limiting)
  reliably apply.
- Treat a null RemoteIpAddress as non-loopback in DevUIAuthFilter; tests
  now set IPAddress.Loopback explicitly when exercising the loopback path.
- Add a DEVUI_AUTH_TOKEN env-var fallback test and a /meta-public test.
- Fix dotnet format: add UTF-8 BOM to new files, simplify a cref in
  DevUIOptions, and drop an unused using in the new test.

* .NET: DevUI: add missing authRequired param XML tag

* .NET: DevUI tests: set loopback/AllowRemoteAccess for null-RemoteIp default

DevUIIntegrationTests use the default TestServer which leaves RemoteIpAddress
null. With the new conservative loopback default those tests now hit 403; set
AllowRemoteAccess on the option since those tests are not exercising access
control. Also add the missing SimulateRemoteIp call in the wrong-bearer test.

* .NET: DevUI tests: capture DEVUI_AUTH_TOKEN before parallel tests can see it

The env-var test was leaking DEVUI_AUTH_TOKEN into parallel DevUIIntegrationTests,
intermittently causing their requests to be rejected as 401. Eagerly resolve the
singleton DevUIAuthFilter so its constructor captures the token, then restore the
env var before any HTTP requests run.

dotnet/src/Microsoft.Agents.AI.DevUI/DevUIAuthFilter.cs

@@ -0,0 +1,106 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Net;
+using System.Security.Cryptography;
+using System.Text;
+using Microsoft.Extensions.Options;
+using Microsoft.Net.Http.Headers;
+
+namespace Microsoft.Agents.AI.DevUI;
+
+/// <summary>
+/// Endpoint filter that enforces the DevUI security posture: loopback-only
+/// access by default, plus optional bearer-token authentication.
+/// </summary>
+internal sealed class DevUIAuthFilter : IEndpointFilter
+{
+    private const string BearerScheme = "Bearer";
+
+    private readonly DevUIOptions _options;
+    private readonly byte[]? _expectedTokenBytes;
+    private readonly ILogger<DevUIAuthFilter> _logger;
+
+    /// <summary>
+    /// Gets a value indicating whether a bearer token is required by this filter
+    /// (either via <see cref="DevUIOptions.AuthToken"/> or the
+    /// <c>DEVUI_AUTH_TOKEN</c> environment variable).
+    /// </summary>
+    public bool TokenRequired => this._expectedTokenBytes is { Length: > 0 };
+
+    public DevUIAuthFilter(IOptions<DevUIOptions> options, ILogger<DevUIAuthFilter> logger)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        ArgumentNullException.ThrowIfNull(logger);
+        this._options = options.Value;
+        this._logger = logger;
+
+        var configuredToken = !string.IsNullOrEmpty(this._options.AuthToken)
+            ? this._options.AuthToken
+            : Environment.GetEnvironmentVariable(DevUIOptions.AuthTokenEnvironmentVariable);
+
+        this._expectedTokenBytes = !string.IsNullOrEmpty(configuredToken)
+            ? Encoding.UTF8.GetBytes(configuredToken)
+            : null;
+    }
+
+    public async ValueTask<object?> InvokeAsync(EndpointFilterInvocationContext context, EndpointFilterDelegate next)
+    {
+        var httpContext = context.HttpContext;
+        var remoteIp = httpContext.Connection.RemoteIpAddress;
+        var isLoopback = remoteIp is not null && IPAddress.IsLoopback(remoteIp);
+
+        if (!isLoopback && !this._options.AllowRemoteAccess)
+        {
+            this._logger.LogWarning(
+                "Rejected non-loopback DevUI request from {RemoteIp}. Set DevUIOptions.AllowRemoteAccess to permit remote callers.",
+                remoteIp);
+            return Results.Problem(
+                statusCode: StatusCodes.Status403Forbidden,
+                title: "DevUI access denied",
+                detail: "DevUI is restricted to loopback callers by default. Enable AllowRemoteAccess to permit remote access.");
+        }
+
+        if (this._expectedTokenBytes is { Length: > 0 } expected && !TokenIsValid(httpContext.Request, expected))
+        {
+            httpContext.Response.Headers[HeaderNames.WWWAuthenticate] = BearerScheme;
+            return Results.Problem(
+                statusCode: StatusCodes.Status401Unauthorized,
+                title: "DevUI authentication required",
+                detail: "Provide a valid bearer token via the Authorization header.");
+        }
+
+        return await next(context).ConfigureAwait(false);
+    }
+
+    private static bool TokenIsValid(HttpRequest request, byte[] expected)
+    {
+        if (!request.Headers.TryGetValue(HeaderNames.Authorization, out var headerValues))
+        {
+            return false;
+        }
+
+        foreach (var header in headerValues)
+        {
+            if (string.IsNullOrEmpty(header))
+            {
+                continue;
+            }
+
+            const int PrefixLength = 7; // "Bearer "
+            if (header.Length <= PrefixLength ||
+                !header.StartsWith(BearerScheme, StringComparison.OrdinalIgnoreCase) ||
+                header[BearerScheme.Length] != ' ')
+            {
+                continue;
+            }
+
+            var presented = Encoding.UTF8.GetBytes(header.AsSpan(PrefixLength).Trim().ToString());
+            if (CryptographicOperations.FixedTimeEquals(presented, expected))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}

dotnet/src/Microsoft.Agents.AI.DevUI/DevUIExtensions.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System.Diagnostics.CodeAnalysis;
+using Microsoft.Extensions.Options;
 
 namespace Microsoft.Agents.AI.DevUI;
 
@@ -13,12 +14,19 @@ public static class DevUIExtensions
     /// Maps an endpoint that serves the DevUI from the '/devui' path.
     /// </summary>
     /// <remarks>
+    /// <para>
     /// DevUI requires the OpenAI Responses and Conversations services to be registered with
     /// <see cref="MicrosoftAgentAIHostingOpenAIServiceCollectionExtensions.AddOpenAIResponses(IServiceCollection)"/> and
     /// <see cref="MicrosoftAgentAIHostingOpenAIServiceCollectionExtensions.AddOpenAIConversations(IServiceCollection)"/>,
     /// and the corresponding endpoints to be mapped using
     /// <see cref="MicrosoftAgentAIHostingOpenAIEndpointRouteBuilderExtensions.MapOpenAIResponses(IEndpointRouteBuilder)"/> and
     /// <see cref="MicrosoftAgentAIHostingOpenAIEndpointRouteBuilderExtensions.MapOpenAIConversations(IEndpointRouteBuilder)"/>.
+    /// </para>
+    /// <para>
+    /// DevUI is restricted to loopback callers unless
+    /// <see cref="DevUIOptions.AllowRemoteAccess"/> is set. See <see cref="DevUIOptions"/>
+    /// for the available authentication and authorization hooks.
+    /// </para>
     /// </remarks>
     /// <param name="endpoints">The <see cref="IEndpointRouteBuilder"/> to add the endpoint to.</param>
     /// <returns>A <see cref="IEndpointConventionBuilder"/> that can be used to add authorization or other endpoint configuration.</returns>
@@ -30,11 +38,29 @@ public static class DevUIExtensions
     public static IEndpointConventionBuilder MapDevUI(
         this IEndpointRouteBuilder endpoints)
     {
-        var group = endpoints.MapGroup("");
-        group.MapDevUI(pattern: "/devui");
-        group.MapMeta();
-        group.MapEntities();
-        return group;
+        ArgumentNullException.ThrowIfNull(endpoints);
+
+        var authFilter = endpoints.ServiceProvider.GetRequiredService<DevUIAuthFilter>();
+        var options = endpoints.ServiceProvider.GetRequiredService<IOptions<DevUIOptions>>().Value;
+        var startupLogger = endpoints.ServiceProvider.GetRequiredService<ILogger<DevUIAuthFilter>>();
+
+        WarnIfInsecurelyExposed(startupLogger, options);
+
+        // /meta must remain reachable without authentication so the frontend can
+        // discover whether a bearer token is required before prompting for one.
+        endpoints.MapMeta(authRequired: authFilter.TokenRequired);
+
+        var protectedGroup = endpoints.MapGroup("");
+
+        // Conventions must be applied before endpoints are added to the group so
+        // they reliably attach to every protected DevUI endpoint.
+        options.ConfigureEndpoints?.Invoke(protectedGroup);
+        protectedGroup.AddEndpointFilter(authFilter);
+
+        protectedGroup.MapDevUI(pattern: "/devui");
+        protectedGroup.MapEntities();
+
+        return protectedGroup;
     }
 
     /// <summary>
@@ -66,4 +92,18 @@ public static class DevUIExtensions
             .WithName($"DevUI at {cleanPattern}")
             .WithDescription("Interactive developer interface for Microsoft Agent Framework");
     }
+
+    private static void WarnIfInsecurelyExposed(ILogger logger, DevUIOptions options)
+    {
+        var tokenConfigured = !string.IsNullOrEmpty(options.AuthToken)
+            || !string.IsNullOrEmpty(Environment.GetEnvironmentVariable(DevUIOptions.AuthTokenEnvironmentVariable));
+
+        if (options.AllowRemoteAccess && !tokenConfigured && options.ConfigureEndpoints is null)
+        {
+            logger.LogWarning(
+                "DevUI is configured with AllowRemoteAccess=true and no authentication. " +
+                "Set DevUIOptions.AuthToken, the {EnvVar} environment variable, or attach an authorization policy via ConfigureEndpoints.",
+                DevUIOptions.AuthTokenEnvironmentVariable);
+        }
+    }
 }

dotnet/src/Microsoft.Agents.AI.DevUI/DevUIOptions.cs

@@ -0,0 +1,59 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace Microsoft.Agents.AI.DevUI;
+
+/// <summary>
+/// Options that control the security posture of the DevUI HTTP surface.
+/// </summary>
+/// <remarks>
+/// DevUI exposes agent metadata that is sensitive in production contexts:
+/// system instructions, tool definitions, model identifiers, and workflow
+/// structure. By default, DevUI rejects any request whose remote endpoint
+/// is not a loopback address. Hosts that intentionally expose DevUI on a
+/// non-loopback interface must opt in via <see cref="AllowRemoteAccess"/>
+/// and should also configure <see cref="AuthToken"/> or
+/// <see cref="ConfigureEndpoints"/> to attach an authorization policy.
+/// </remarks>
+public sealed class DevUIOptions
+{
+    /// <summary>
+    /// Environment variable inspected for a default bearer token when
+    /// <see cref="AuthToken"/> is not explicitly set.
+    /// </summary>
+    public const string AuthTokenEnvironmentVariable = "DEVUI_AUTH_TOKEN";
+
+    /// <summary>
+    /// Gets or sets a value indicating whether DevUI may be served to
+    /// non-loopback callers. Defaults to <see langword="false"/>.
+    /// </summary>
+    /// <remarks>
+    /// When <see langword="false"/>, any request whose
+    /// <see cref="ConnectionInfo.RemoteIpAddress"/> is
+    /// not a loopback address (or is missing) is rejected with HTTP 403 before
+    /// reaching the DevUI handlers. Enable only when the host is responsible
+    /// for fronting DevUI with its own authentication, network policy, or both.
+    /// </remarks>
+    public bool AllowRemoteAccess { get; set; }
+
+    /// <summary>
+    /// Gets or sets a shared bearer token required on every DevUI request.
+    /// When <see langword="null"/> or empty, the value of the
+    /// <c>DEVUI_AUTH_TOKEN</c> environment variable is used instead.
+    /// </summary>
+    /// <remarks>
+    /// When a token is configured, requests must include the header
+    /// <c>Authorization: Bearer &lt;token&gt;</c>. Comparison is performed
+    /// in constant time. This is a convenience for development scenarios.
+    /// Production hosts should prefer a real ASP.NET Core authentication
+    /// scheme attached via <see cref="ConfigureEndpoints"/>.
+    /// </remarks>
+    public string? AuthToken { get; set; }
+
+    /// <summary>
+    /// Gets or sets a callback invoked with the DevUI endpoint group so the
+    /// host can attach authorization, rate limiting, or other endpoint
+    /// conventions (for example
+    /// <c>group.RequireAuthorization("DevUIPolicy")</c>).
+    /// </summary>
+    public Action<IEndpointConventionBuilder>? ConfigureEndpoints { get; set; }
+}

dotnet/src/Microsoft.Agents.AI.DevUI/HostApplicationBuilderExtensions.cs

@@ -1,5 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using Microsoft.Agents.AI.DevUI;
+
 namespace Microsoft.Extensions.Hosting;
 
 /// <summary>
@@ -13,10 +15,19 @@ public static class MicrosoftAgentAIDevUIHostApplicationBuilderExtensions
     /// <param name="builder">The <see cref="IHostApplicationBuilder"/> to configure.</param>
     /// <returns>The <see cref="IHostApplicationBuilder"/> for method chaining.</returns>
     public static IHostApplicationBuilder AddDevUI(this IHostApplicationBuilder builder)
+        => AddDevUI(builder, configure: null);
+
+    /// <summary>
+    /// Adds DevUI services to the host application builder.
+    /// </summary>
+    /// <param name="builder">The <see cref="IHostApplicationBuilder"/> to configure.</param>
+    /// <param name="configure">Optional callback used to configure <see cref="DevUIOptions"/>.</param>
+    /// <returns>The <see cref="IHostApplicationBuilder"/> for method chaining.</returns>
+    public static IHostApplicationBuilder AddDevUI(this IHostApplicationBuilder builder, Action<DevUIOptions>? configure)
     {
         ArgumentNullException.ThrowIfNull(builder);
 
-        builder.Services.AddDevUI();
+        builder.Services.AddDevUI(configure);
 
         return builder;
     }

dotnet/src/Microsoft.Agents.AI.DevUI/MetaApiExtensions.cs

@@ -13,6 +13,7 @@ internal static class MetaApiExtensions
     /// Maps the HTTP API endpoint for retrieving server metadata.
     /// </summary>
     /// <param name="endpoints">The <see cref="IEndpointRouteBuilder"/> to add the route to.</param>
+    /// <param name="authRequired">Value reported via <c>auth_required</c> in the meta response so the frontend can decide whether to prompt for a bearer token.</param>
     /// <returns>The <see cref="IEndpointConventionBuilder"/> for method chaining.</returns>
     /// <remarks>
     /// This extension method registers the following endpoint:
@@ -22,16 +23,16 @@ internal static class MetaApiExtensions
     /// The endpoint is compatible with the Python DevUI frontend and provides essential
     /// configuration information needed for proper frontend initialization.
     /// </remarks>
-    public static IEndpointConventionBuilder MapMeta(this IEndpointRouteBuilder endpoints)
+    public static IEndpointConventionBuilder MapMeta(this IEndpointRouteBuilder endpoints, bool authRequired = false)
     {
-        return endpoints.MapGet("/meta", GetMeta)
+        return endpoints.MapGet("/meta", () => GetMeta(authRequired))
             .WithName("GetMeta")
             .WithSummary("Get server metadata and configuration")
             .WithDescription("Returns server metadata including UI mode, version, framework identifier, capabilities, and authentication requirements. Used by the frontend for initialization and feature detection.")
             .Produces<MetaResponse>(StatusCodes.Status200OK, contentType: "application/json");
     }
 
-    private static IResult GetMeta()
+    private static IResult GetMeta(bool authRequired)
     {
         // TODO: Consider making these configurable via IOptions<DevUIOptions>
         // For now, using sensible defaults that match Python DevUI behavior
@@ -53,7 +54,7 @@ internal static class MetaApiExtensions
                 // Deployment capability - not currently supported in .NET DevUI
                 ["deployment"] = false
             },
-            AuthRequired = false // Could be made configurable based on authentication middleware
+            AuthRequired = authRequired
         };
 
         return Results.Json(meta, EntitiesJsonContext.Default.MetaResponse);

dotnet/src/Microsoft.Agents.AI.DevUI/README.md

@@ -2,6 +2,9 @@
 
 This package provides a web interface for testing and debugging AI agents during development.
 
+> [!WARNING]
+> DevUI is intended for development only. Its endpoints surface agent system instructions, tool definitions, model identifiers, and workflow structure. Do not expose DevUI to untrusted callers. By default, DevUI rejects any request whose remote endpoint is not a loopback address; see [Security](#security) below for the available options.
+
 ## Installation
 
 ```bash
@@ -48,3 +51,30 @@ if (builder.Environment.IsDevelopment())
 
 app.Run();
 ```
+
+## Security
+
+DevUI exposes `/v1/entities` and `/v1/entities/{id}/info`, which return agent metadata including the system prompt (`ChatClientAgent.Instructions`). To prevent accidental disclosure, the DevUI route group is wrapped in a small endpoint filter that:
+
+- Rejects requests from any non-loopback `RemoteIpAddress` with HTTP 403 by default.
+- Optionally requires a shared bearer token on every request.
+
+Configure via `DevUIOptions`:
+
+```csharp
+builder.AddDevUI(options =>
+{
+    // Allow non-loopback callers. Set this only when the host fronts DevUI with
+    // its own authentication or network policy.
+    options.AllowRemoteAccess = true;
+
+    // Optional: require Authorization: Bearer <token> on every request.
+    // Falls back to the DEVUI_AUTH_TOKEN environment variable when null.
+    options.AuthToken = builder.Configuration["DevUI:AuthToken"];
+
+    // Optional: attach a real authorization policy or rate limiting.
+    options.ConfigureEndpoints = group => group.RequireAuthorization("DevUIPolicy");
+});
+```
+
+The bundled bearer-token check uses constant-time comparison and is intended as a convenience for development scenarios. Production hosts should prefer a real ASP.NET Core authentication scheme via `ConfigureEndpoints`.

dotnet/src/Microsoft.Agents.AI.DevUI/ServiceCollectionsExtensions.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using Microsoft.Agents.AI;
+using Microsoft.Agents.AI.DevUI;
 using Microsoft.Agents.AI.Workflows;
 using Microsoft.Shared.Diagnostics;
 
@@ -17,9 +18,26 @@ public static class MicrosoftAgentAIDevUIServiceCollectionsExtensions
     /// <param name="services">The <see cref="IServiceCollection"/> to configure.</param>
     /// <returns>The <see cref="IServiceCollection"/> for method chaining.</returns>
     public static IServiceCollection AddDevUI(this IServiceCollection services)
+        => AddDevUI(services, configure: null);
+
+    /// <summary>
+    /// Adds services required for DevUI integration.
+    /// </summary>
+    /// <param name="services">The <see cref="IServiceCollection"/> to configure.</param>
+    /// <param name="configure">Optional callback used to configure <see cref="DevUIOptions"/>.</param>
+    /// <returns>The <see cref="IServiceCollection"/> for method chaining.</returns>
+    public static IServiceCollection AddDevUI(this IServiceCollection services, Action<DevUIOptions>? configure)
     {
         ArgumentNullException.ThrowIfNull(services);
 
+        var optionsBuilder = services.AddOptions<DevUIOptions>();
+        if (configure is not null)
+        {
+            optionsBuilder.Configure(configure);
+        }
+
+        services.AddSingleton<DevUIAuthFilter>();
+
         // a factory that tries to construct an AIAgent from Workflow,
         // even if workflow was not explicitly registered as an AIAgent.
 

dotnet/tests/Microsoft.Agents.AI.DevUI.UnitTests/DevUIAccessControlTests.cs

@@ -0,0 +1,183 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Net;
+using System.Net.Http;
+using System.Net.Http.Headers;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.TestHost;
+using Microsoft.Extensions.AI;
+using Microsoft.Extensions.DependencyInjection;
+using Moq;
+
+namespace Microsoft.Agents.AI.DevUI.UnitTests;
+
+public class DevUIAccessControlTests
+{
+    private static WebApplicationBuilder NewBuilder()
+    {
+        var builder = WebApplication.CreateBuilder();
+        builder.WebHost.UseTestServer();
+
+        var mockChatClient = new Mock<IChatClient>();
+        var agent = new ChatClientAgent(mockChatClient.Object, "Test", "agent-name");
+        builder.Services.AddKeyedSingleton<AIAgent>("agent-name", agent);
+
+        return builder;
+    }
+
+    private static void SimulateRemoteIp(WebApplication app, IPAddress remoteIp)
+    {
+        app.Use(async (HttpContext ctx, RequestDelegate next) =>
+        {
+            ctx.Connection.RemoteIpAddress = remoteIp;
+            await next(ctx);
+        });
+    }
+
+    [Fact]
+    public async Task NonLoopbackRequest_ReturnsForbiddenByDefaultAsync()
+    {
+        var builder = NewBuilder();
+        builder.Services.AddDevUI();
+
+        using var app = builder.Build();
+        SimulateRemoteIp(app, IPAddress.Parse("192.0.2.1"));
+        app.MapDevUI();
+        await app.StartAsync();
+
+        var response = await app.GetTestClient().GetAsync(new Uri("/v1/entities", UriKind.Relative));
+
+        Assert.Equal(HttpStatusCode.Forbidden, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task NonLoopbackRequest_IsAllowedWhenAllowRemoteAccessAsync()
+    {
+        var builder = NewBuilder();
+        builder.Services.AddDevUI(o => o.AllowRemoteAccess = true);
+
+        using var app = builder.Build();
+        SimulateRemoteIp(app, IPAddress.Parse("192.0.2.1"));
+        app.MapDevUI();
+        await app.StartAsync();
+
+        var response = await app.GetTestClient().GetAsync(new Uri("/v1/entities", UriKind.Relative));
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task LoopbackRequest_WithAuthTokenSet_RequiresBearerHeaderAsync()
+    {
+        var builder = NewBuilder();
+        builder.Services.AddDevUI(o => o.AuthToken = "secret-token");
+
+        using var app = builder.Build();
+        SimulateRemoteIp(app, IPAddress.Loopback);
+        app.MapDevUI();
+        await app.StartAsync();
+
+        var response = await app.GetTestClient().GetAsync(new Uri("/v1/entities", UriKind.Relative));
+
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task LoopbackRequest_WithCorrectBearerToken_SucceedsAsync()
+    {
+        var builder = NewBuilder();
+        builder.Services.AddDevUI(o => o.AuthToken = "secret-token");
+
+        using var app = builder.Build();
+        SimulateRemoteIp(app, IPAddress.Loopback);
+        app.MapDevUI();
+        await app.StartAsync();
+
+        using var request = new HttpRequestMessage(HttpMethod.Get, new Uri("/v1/entities", UriKind.Relative));
+        request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", "secret-token");
+        var response = await app.GetTestClient().SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task EnvironmentVariableToken_IsEnforcedWhenAuthTokenNotConfiguredAsync()
+    {
+        const string EnvVar = "DEVUI_AUTH_TOKEN";
+        const string EnvToken = "env-token";
+        var previous = Environment.GetEnvironmentVariable(EnvVar);
+        Environment.SetEnvironmentVariable(EnvVar, EnvToken);
+
+        WebApplication? app = null;
+        try
+        {
+            var builder = NewBuilder();
+            builder.Services.AddDevUI();
+
+            app = builder.Build();
+
+            // Force singleton construction so the env var is captured before we
+            // restore it; otherwise tests running in parallel can pick up the
+            // leaked DEVUI_AUTH_TOKEN.
+            _ = app.Services.GetRequiredService<DevUIAuthFilter>();
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable(EnvVar, previous);
+        }
+
+        await using (app)
+        {
+            SimulateRemoteIp(app, IPAddress.Loopback);
+            app.MapDevUI();
+            await app.StartAsync();
+
+            var missing = await app.GetTestClient().GetAsync(new Uri("/v1/entities", UriKind.Relative));
+            Assert.Equal(HttpStatusCode.Unauthorized, missing.StatusCode);
+
+            using var request = new HttpRequestMessage(HttpMethod.Get, new Uri("/v1/entities", UriKind.Relative));
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", EnvToken);
+            var accepted = await app.GetTestClient().SendAsync(request);
+            Assert.Equal(HttpStatusCode.OK, accepted.StatusCode);
+        }
+    }
+
+    [Fact]
+    public async Task MetaEndpoint_IsReachableWithoutAuthenticationAsync()
+    {
+        var builder = NewBuilder();
+        builder.Services.AddDevUI(o => o.AuthToken = "secret-token");
+
+        using var app = builder.Build();
+        SimulateRemoteIp(app, IPAddress.Loopback);
+        app.MapDevUI();
+        await app.StartAsync();
+
+        var response = await app.GetTestClient().GetAsync(new Uri("/meta", UriKind.Relative));
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        var body = await response.Content.ReadAsStringAsync();
+        Assert.Contains("\"auth_required\":true", body);
+    }
+
+    [Fact]
+    public async Task LoopbackRequest_WithWrongBearerToken_ReturnsUnauthorizedAsync()
+    {
+        var builder = NewBuilder();
+        builder.Services.AddDevUI(o => o.AuthToken = "secret-token");
+
+        using var app = builder.Build();
+        SimulateRemoteIp(app, IPAddress.Loopback);
+        app.MapDevUI();
+        await app.StartAsync();
+
+        using var request = new HttpRequestMessage(HttpMethod.Get, new Uri("/v1/entities", UriKind.Relative));
+        request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", "not-the-token");
+        var response = await app.GetTestClient().SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+    }
+}

dotnet/tests/Microsoft.Agents.AI.DevUI.UnitTests/DevUIIntegrationTests.cs

@@ -33,7 +33,7 @@ public class DevUIIntegrationTests
         var agent = new ChatClientAgent(mockChatClient.Object, "Test", "agent-name");
 
         builder.Services.AddKeyedSingleton<AIAgent>("registration-key", agent);
-        builder.Services.AddDevUI();
+        builder.Services.AddDevUI(o => o.AllowRemoteAccess = true);
 
         using WebApplication app = builder.Build();
         app.MapDevUI();
@@ -66,7 +66,7 @@ public class DevUIIntegrationTests
         builder.Services.AddKeyedSingleton<AIAgent>("key-1", agent1);
         builder.Services.AddKeyedSingleton<AIAgent>("key-2", agent2);
         builder.Services.AddKeyedSingleton<AIAgent>("key-3", agent3);
-        builder.Services.AddDevUI();
+        builder.Services.AddDevUI(o => o.AllowRemoteAccess = true);
 
         using WebApplication app = builder.Build();
         app.MapDevUI();
@@ -102,7 +102,7 @@ public class DevUIIntegrationTests
         builder.Services.AddKeyedSingleton<AIAgent>("key-1", agentKeyed1);
         builder.Services.AddKeyedSingleton<AIAgent>("key-2", agentKeyed2);
         builder.Services.AddSingleton<AIAgent>(agentDefault);
-        builder.Services.AddDevUI();
+        builder.Services.AddDevUI(o => o.AllowRemoteAccess = true);
 
         using WebApplication app = builder.Build();
         app.MapDevUI();
@@ -151,7 +151,7 @@ public class DevUIIntegrationTests
         builder.Services.AddKeyedSingleton("key-1", workflow1);
         builder.Services.AddKeyedSingleton("key-2", workflow2);
         builder.Services.AddKeyedSingleton("key-3", workflow3);
-        builder.Services.AddDevUI();
+        builder.Services.AddDevUI(o => o.AllowRemoteAccess = true);
 
         using WebApplication app = builder.Build();
         app.MapDevUI();
@@ -197,7 +197,7 @@ public class DevUIIntegrationTests
         builder.Services.AddKeyedSingleton("key-1", workflowKeyed1);
         builder.Services.AddKeyedSingleton("key-2", workflowKeyed2);
         builder.Services.AddSingleton(workflowDefault);
-        builder.Services.AddDevUI();
+        builder.Services.AddDevUI(o => o.AllowRemoteAccess = true);
 
         using WebApplication app = builder.Build();
         app.MapDevUI();
@@ -255,7 +255,7 @@ public class DevUIIntegrationTests
         builder.Services.AddKeyedSingleton("workflow-key-1", workflow1);
         builder.Services.AddKeyedSingleton("workflow-key-2", workflow2);
         builder.Services.AddSingleton(workflowDefault);
-        builder.Services.AddDevUI();
+        builder.Services.AddDevUI(o => o.AllowRemoteAccess = true);
 
         using WebApplication app = builder.Build();
         app.MapDevUI();