.NET: Implement Purview middleware in dotnet (#1949)

* Move Purview integration logic into middleware

* Improve error handling and user id management

* Rename purview package

* Handle 402s more explicitly; add Middleware generation methods; don't ignore exceptions

* Use DI container; pass scope id to PC

* Add protection scope caching

* Wrap more exceptions in PurviewClient

* Remove block check dedup; add tests

* Refactor PurviewWrapper intialization; Add unit tests

* Use different .Use method and add IDisposable stub

* Add background job processing for Purview

* Misc comment cleanup

* Apply copilot comments

* Fix formatting

* Formatting other files to fix pipeline

* Small updates to settings and exceptions

* Add README

* Move Purview sample

* Address review comments and update XML comments

* Newline after namespace

* Move public Purview classes to single namespace; Clean up csproj and slnx

* Commit the renames

* Remove unused openAI dependency

---------

Co-authored-by: Dmytro Struk <13853051+dmytrostruk@users.noreply.github.com>

dotnet/samples/Purview/AgentWithPurview/AgentWithPurview.csproj

@@ -0,0 +1,21 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net9.0</TargetFramework>
+
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Azure.AI.OpenAI" />
+    <PackageReference Include="Azure.Identity" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\src\Microsoft.Agents.AI.OpenAI\Microsoft.Agents.AI.OpenAI.csproj" />
+    <ProjectReference Include="..\..\..\src\Microsoft.Agents.AI.Purview\Microsoft.Agents.AI.Purview.csproj" />
+  </ItemGroup>
+
+</Project>

dotnet/samples/Purview/AgentWithPurview/Program.cs

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+// Copyright (c) Microsoft. All rights reserved.
+
+// This sample shows how to create and use a simple AI agent with Purview integration.
+// It uses Azure OpenAI as the backend, but any IChatClient can be used.
+// Authentication to Purview is done using an InteractiveBrowserCredential.
+// Any TokenCredential with Purview API permissions can be used here.
+
+using Azure.AI.OpenAI;
+using Azure.Core;
+using Azure.Identity;
+using Microsoft.Agents.AI;
+using Microsoft.Agents.AI.Purview;
+using Microsoft.Extensions.AI;
+
+var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var purviewClientAppId = Environment.GetEnvironmentVariable("PURVIEW_CLIENT_APP_ID") ?? throw new InvalidOperationException("PURVIEW_CLIENT_APP_ID is not set.");
+
+// This will get a user token for an entra app configured to call the Purview API.
+// Any TokenCredential with permissions to call the Purview API can be used here.
+TokenCredential browserCredential = new InteractiveBrowserCredential(
+    new InteractiveBrowserCredentialOptions
+    {
+        ClientId = purviewClientAppId
+    });
+
+using IChatClient client = new AzureOpenAIClient(
+    new Uri(endpoint),
+    new AzureCliCredential())
+    .GetOpenAIResponseClient(deploymentName)
+    .AsIChatClient()
+    .AsBuilder()
+    .WithPurview(browserCredential, new PurviewSettings("Agent Framework Test App"))
+    .Build();
+
+Console.WriteLine("Enter a prompt to send to the client:");
+string? promptText = Console.ReadLine();
+
+if (!string.IsNullOrEmpty(promptText))
+{
+    // Invoke the agent and output the text result.
+    Console.WriteLine(await client.GetResponseAsync(promptText));
+}