.NET: Add sample for per-run refreshable MCP authentication headers

dotnet/agent-framework-dotnet.slnx

@@ -217,6 +217,7 @@
   <Folder Name="/Samples/02-agents/ModelContextProtocol/">
     <File Path="samples/02-agents/ModelContextProtocol/README.md" />
     <Project Path="samples/02-agents/ModelContextProtocol/Agent_MCP_LongRunningTask_Client/Agent_MCP_LongRunningTask_Client.csproj" />
+    <Project Path="samples/02-agents/ModelContextProtocol/Agent_MCP_PerRun_AuthHeaders/Agent_MCP_PerRun_AuthHeaders.csproj" />
     <Project Path="samples/02-agents/ModelContextProtocol/Agent_MCP_Server/Agent_MCP_Server.csproj" />
     <Project Path="samples/02-agents/ModelContextProtocol/Agent_MCP_Server_Auth/Agent_MCP_Server_Auth.csproj" />
     <Project Path="samples/02-agents/ModelContextProtocol/FoundryAgent_Hosted_MCP/FoundryAgent_Hosted_MCP.csproj" />

dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_PerRun_AuthHeaders/Agent_MCP_PerRun_AuthHeaders.csproj

@@ -0,0 +1,21 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFrameworks>net10.0</TargetFrameworks>
+
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Azure.Identity" />
+    <PackageReference Include="ModelContextProtocol" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\..\src\Microsoft.Agents.AI\Microsoft.Agents.AI.csproj" />
+    <ProjectReference Include="..\..\..\..\src\Microsoft.Agents.AI.Foundry\Microsoft.Agents.AI.Foundry.csproj" />
+  </ItemGroup>
+
+</Project>

dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_PerRun_AuthHeaders/Program.cs

@@ -0,0 +1,133 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+// This sample shows how to attach per-run (refreshable) authentication headers to MCP requests.
+//
+// The agent connects to an MCP server with a custom HttpClient. A DelegatingHandler reads a token
+// for the current run from an AsyncLocal scope and stamps it on each outbound MCP request, so a
+// short-lived token (for example an OBO or cloud identity token that expires) can be refreshed on
+// every run without rebuilding the agent or the MCP connection.
+//
+// The agent backend is Microsoft Foundry via the Responses API (RAPI). The MCP server is the public
+// Microsoft Learn MCP server, which ignores the demonstration token; in production you point the
+// handler at your own protected MCP server and mint a real token per run.
+
+using System.Net.Http.Headers;
+using Azure.AI.Projects;
+using Azure.Identity;
+using Microsoft.Agents.AI;
+using Microsoft.Extensions.AI;
+using ModelContextProtocol.Client;
+
+var projectEndpoint = new Uri(Environment.GetEnvironmentVariable("FOUNDRY_PROJECT_ENDPOINT")
+    ?? throw new InvalidOperationException("FOUNDRY_PROJECT_ENDPOINT is not set."));
+var deploymentName = Environment.GetEnvironmentVariable("FOUNDRY_MODEL") ?? "gpt-5.4-mini";
+
+var serverEndpoint = new Uri("https://learn.microsoft.com/api/mcp");
+
+// Custom HttpClient for the MCP transport. The per-run handler attaches the bearer; the inner
+// handler disables cookies (no cross-context state) and checks certificate revocation.
+using var httpClient = new HttpClient(new PerRunAuthHeaderHandler(serverEndpoint)
+{
+    InnerHandler = new HttpClientHandler
+    {
+        UseCookies = false,
+        CheckCertificateRevocationList = true,
+    },
+});
+
+Console.WriteLine($"Connecting to MCP server at {serverEndpoint} ...");
+
+await using var mcpClient = await McpClient.CreateAsync(new HttpClientTransport(new()
+{
+    Endpoint = serverEndpoint,
+    Name = "Microsoft Learn MCP",
+    TransportMode = HttpTransportMode.StreamableHttp,
+}, httpClient));
+
+IList<McpClientTool> mcpTools = await mcpClient.ListToolsAsync();
+Console.WriteLine($"MCP tools available: {string.Join(", ", mcpTools.Select(t => t.Name))}");
+
+// Build the agent from Microsoft Foundry using the Responses API (RAPI).
+// WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
+// In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
+// latency issues, unintended credential probing, and potential security risks from fallback mechanisms.
+AIAgent agent = new AIProjectClient(projectEndpoint, new DefaultAzureCredential())
+    .AsAIAgent(
+        model: deploymentName,
+        instructions: "You answer Microsoft documentation questions using the available tools.",
+        name: "DocsAgent",
+        tools: [.. mcpTools.Cast<AITool>()]);
+
+// Run the same agent twice under two different contexts. Each run gets a freshly minted token,
+// proving the auth header is per-run rather than bound when the agent or MCP connection was created.
+await RunForContextAsync(agent, "tenant-a", "How do I create an Azure storage account with az cli?");
+await RunForContextAsync(agent, "tenant-b", "What is Azure Functions?");
+
+static async Task RunForContextAsync(AIAgent agent, string label, string prompt)
+{
+    // Stand-in for a real per-run token (for example an OBO or cloud identity token).
+    // It carries no PII and is regenerated on every run. The label is non-secret and used for logging.
+    McpRunScope.Current = new McpRunContext(label, $"{label}.{Guid.NewGuid():N}");
+    try
+    {
+        Console.WriteLine($"\n=== Run for '{label}' (fresh per-run token) ===");
+        Console.WriteLine(await agent.RunAsync(prompt));
+    }
+    finally
+    {
+        // Clear the scope so a token never bleeds into later, unrelated work.
+        McpRunScope.Current = null;
+    }
+}
+
+/// <summary>
+/// Carries the context for the current run. <see cref="Label"/> is a non-secret identifier safe to
+/// log; <see cref="Token"/> is the secret that must never be logged or persisted.
+/// </summary>
+internal sealed record McpRunContext(string Label, string Token);
+
+/// <summary>
+/// Flows the current <see cref="McpRunContext"/> to the MCP <see cref="DelegatingHandler"/> without
+/// threading it through every call. Set it before a run and reset it afterwards.
+/// </summary>
+internal static class McpRunScope
+{
+    private static readonly AsyncLocal<McpRunContext?> s_current = new();
+
+    public static McpRunContext? Current
+    {
+        get => s_current.Value;
+        set => s_current.Value = value;
+    }
+}
+
+/// <summary>
+/// Attaches the current run's bearer token to outbound MCP requests. The token is read fresh on
+/// every request, so refreshing it between runs needs no agent or connection rebuild.
+/// </summary>
+/// <remarks>
+/// Security: the bearer is attached only over HTTPS and only when the request targets the configured
+/// MCP server origin, which prevents the credential from leaking over plaintext or to a redirect
+/// target on another origin. Only the non-secret label is logged, never the token.
+/// </remarks>
+internal sealed class PerRunAuthHeaderHandler(Uri serverEndpoint) : DelegatingHandler
+{
+    private readonly string _serverOrigin = serverEndpoint.GetLeftPart(UriPartial.Authority);
+
+    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+    {
+        McpRunContext? context = McpRunScope.Current;
+        Uri? requestUri = request.RequestUri;
+
+        if (context is not null
+            && requestUri is not null
+            && requestUri.Scheme == Uri.UriSchemeHttps
+            && string.Equals(requestUri.GetLeftPart(UriPartial.Authority), this._serverOrigin, StringComparison.OrdinalIgnoreCase))
+        {
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", context.Token);
+            Console.WriteLine($"[mcp-auth] attached bearer for '{context.Label}' -> {request.Method} {requestUri.AbsolutePath}");
+        }
+
+        return await base.SendAsync(request, cancellationToken).ConfigureAwait(false);
+    }
+}

dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_PerRun_AuthHeaders/README.md

@@ -0,0 +1,88 @@
+# Per-Run MCP Authentication Headers
+
+This sample shows how to attach per-run (refreshable) authentication headers to Model Context
+Protocol (MCP) requests using existing Agent Framework primitives. It addresses scenarios where the
+header value changes from one run to the next, for example a short-lived On-Behalf-Of (OBO) or cloud
+identity token that expires and must be refreshed.
+
+The agent backend is Microsoft Foundry accessed through the Responses API (RAPI). The MCP server is
+the public Microsoft Learn MCP server.
+
+## What this sample demonstrates
+
+- A custom `HttpClient` on the MCP transport whose `DelegatingHandler` stamps an `Authorization`
+  header on every outbound MCP request.
+- An `AsyncLocal` scope (`McpRunScope`) that carries the current run's context to the handler, set
+  immediately before each run and cleared in a `finally` block.
+- Running the same agent twice under two different contexts, each with a freshly minted token, so the
+  header is per-run rather than fixed when the agent or the MCP connection was created.
+
+Because the handler reads the token fresh on every request, an expiring token is refreshed simply by
+placing a new value in scope before the next run. No agent or connection rebuild is required.
+
+## How it works
+
+```text
+RunForContextAsync sets McpRunScope.Current
+        -> agent.RunAsync invokes an MCP tool
+                -> PerRunAuthHeaderHandler reads McpRunScope.Current
+                        -> stamps Authorization: Bearer <token> on the MCP request
+RunForContextAsync clears McpRunScope.Current in finally
+```
+
+The public Microsoft Learn MCP server is anonymous and ignores the demonstration token. In production
+you point the handler at your own protected MCP server and mint a real token per run.
+
+## Prerequisites
+
+- .NET 10 SDK or later
+- A Microsoft Foundry project endpoint and a model deployment
+- An authenticated Azure identity (for example, sign in with `az login`)
+
+Set the following environment variables:
+
+```powershell
+$env:FOUNDRY_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
+$env:FOUNDRY_MODEL="gpt-5.4-mini"
+```
+
+## Run the sample
+
+```powershell
+dotnet run
+```
+
+## Security considerations
+
+This sample is written to demonstrate the pattern safely. When you adapt it, keep these in place:
+
+- **Never log the token.** Only the non-secret label is printed. Avoid printing the token even in a
+  masked form.
+- **Attach the header over HTTPS only.** The handler skips the header when the request is not HTTPS,
+  so a credential is never sent over plaintext.
+- **Scope the header to the MCP server origin.** The handler attaches the header only when the
+  request targets the configured server origin (scheme, host, and port). This prevents the token from
+  being sent to a redirect target on another origin.
+- **Reset the scope after each run.** `McpRunScope.Current` is cleared in a `finally` block so a token
+  does not bleed into later, unrelated work.
+- **Disable cookies on the shared handler.** `UseCookies = false` avoids cross-context state on a
+  shared client, and `CheckCertificateRevocationList = true` validates the server certificate.
+- **Use non-identifying labels and tokens.** The labels and tokens here carry no personal data and are
+  regenerated per run.
+- **Do not persist secrets in serialized session state.** Agent session state is serializable, so keep
+  raw tokens in memory or mint them per run rather than storing them there.
+
+## Production notes
+
+- Replace the demonstration token with a real per-request exchange inside the handler, for example an
+  Azure `TokenCredential`, MSAL OBO flow, or a cloud identity token. Performing the exchange per
+  request lets expiry self-heal because each request obtains a current token.
+- The `AsyncLocal` scope isolates concurrent runs from each other, so parallel runs with different
+  tokens do not interfere.
+- As an alternative carrier, the token can be read from `AgentSession` state by an `AIContextProvider`
+  that copies it into the scope at the start of each invocation. Remember the serialized-state warning
+  above and avoid persisting the raw secret.
+- For MCP servers that implement standard OAuth, `HttpClientTransportOptions.OAuth` already handles the
+  authorization and refresh flow, so a custom handler is unnecessary.
+- This sample attaches the same header for every tool call in a run. Selecting different headers based
+  on the specific tool or its arguments is intentionally out of scope here.

dotnet/samples/02-agents/ModelContextProtocol/README.md

@@ -21,6 +21,7 @@ Before you begin, ensure you have the following prerequisites:
 |---|---|
 |[Agent with MCP server tools](./Agent_MCP_Server/)|This sample demonstrates how to use MCP server tools with a simple agent|
 |[Agent with MCP server tools and authorization](./Agent_MCP_Server_Auth/)|This sample demonstrates how to use MCP Server tools from a protected MCP server with a simple agent|
+|[Agent with per-run MCP authentication headers](./Agent_MCP_PerRun_AuthHeaders/)|This sample demonstrates how to attach per-run, refreshable authentication headers to MCP requests using a custom HttpClient handler and an AsyncLocal scope|
 |[Responses Agent with Hosted MCP tool](./ResponseAgent_Hosted_MCP/)|This sample demonstrates how to use the Hosted MCP tool with the Responses Service, where the service invokes any MCP tools directly|
 |[Agent with long-running MCP task (transparent polling)](./Agent_MCP_LongRunningTask_Client/)|This sample demonstrates how an agent transparently drives a long-running MCP task (SEP-2663) to completion. The wrapper polls the task internally on both `RunAsync` and `RunStreamingAsync` invocations.|