.Net Agents - Refine client provider/factory (#10616)

### Motivation and Context
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Move away from the "client-provider" pattern and make client factory
more discoverable.

Fixes: #10582

### Description
<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

Expose ability to create an SDK client as a static factory methods on
the agent. This is more discoverable than poking around for the
client-provider and aligns with the Python approach.

- Organized factory code in a separate file from the core agent
abstractions.
- Updated samples

### Contribution Checklist
<!-- Before submitting this PR, please make sure: -->

- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [X] I didn't break anyone 😄

dotnet/src/Agents/AzureAI/AzureAIAgent.ClientFactory.cs

@@ -0,0 +1,65 @@
+// Copyright (c) Microsoft. All rights reserved.
+using System.Net.Http;
+using Azure.AI.Projects;
+using Azure.Core;
+using Azure.Core.Pipeline;
+using Microsoft.SemanticKernel.Http;
+
+namespace Microsoft.SemanticKernel.Agents.AzureAI;
+
+/// <summary>
+/// Provides an <see cref="AIProjectClient"/> for use by <see cref="AzureAIAgent"/>.
+/// </summary>
+public sealed partial class AzureAIAgent : KernelAgent
+{
+    /// <summary>
+    /// Produces a <see cref="AIProjectClient"/>.
+    /// </summary>
+    /// <param name="connectionString">The Azure AI Foundry project connection string, in the form `endpoint;subscription_id;resource_group_name;project_name`.</param>
+    /// <param name="credential"> A credential used to authenticate to an Azure Service.</param>
+    /// <param name="httpClient">A custom <see cref="HttpClient"/> for HTTP requests.</param>
+    public static AIProjectClient CreateAzureAIClient(
+        string connectionString,
+        TokenCredential credential,
+        HttpClient? httpClient = null)
+    {
+        Verify.NotNullOrWhiteSpace(connectionString, nameof(connectionString));
+        Verify.NotNull(credential, nameof(credential));
+
+        AIProjectClientOptions clientOptions = CreateAzureClientOptions(httpClient);
+
+        return new AIProjectClient(connectionString, credential, clientOptions);
+    }
+
+    private static AIProjectClientOptions CreateAzureClientOptions(HttpClient? httpClient)
+    {
+        AIProjectClientOptions options =
+            new()
+            {
+                Diagnostics = {
+                    ApplicationId = HttpHeaderConstant.Values.UserAgent,
+                }
+            };
+
+        options.AddPolicy(new SemanticKernelHeadersPolicy(), HttpPipelinePosition.PerCall);
+
+        if (httpClient is not null)
+        {
+            options.Transport = new HttpClientTransport(httpClient);
+            // Disable retry policy if and only if a custom HttpClient is provided.
+            options.RetryPolicy = new RetryPolicy(maxRetries: 0);
+        }
+
+        return options;
+    }
+
+    private class SemanticKernelHeadersPolicy : HttpPipelineSynchronousPolicy
+    {
+        public override void OnSendingRequest(HttpMessage message)
+        {
+            message.Request.Headers.Add(
+                HttpHeaderConstant.Names.SemanticKernelVersion,
+                HttpHeaderConstant.Values.GetAssemblyVersion(typeof(AzureAIAgent)));
+        }
+    }
+}

dotnet/src/Agents/AzureAI/AzureAIAgent.cs

@@ -15,7 +15,7 @@ namespace Microsoft.SemanticKernel.Agents.AzureAI;
 /// <summary>
 /// Provides a specialized <see cref="KernelAgent"/> based on an Azure AI agent.
 /// </summary>
-public sealed class AzureAIAgent : KernelAgent
+public sealed partial class AzureAIAgent : KernelAgent
 {
     /// <summary>
     /// Provides tool definitions used when associating a file attachment to an input message:

dotnet/src/Agents/OpenAI/OpenAIAssistantAgent.ClientFactory.cs

@@ -0,0 +1,122 @@
+// Copyright (c) Microsoft. All rights reserved.
+using System;
+using System.ClientModel;
+using System.ClientModel.Primitives;
+using System.Net.Http;
+using System.Threading;
+using Azure.AI.OpenAI;
+using Azure.Core;
+using Microsoft.SemanticKernel.Http;
+using OpenAI;
+
+namespace Microsoft.SemanticKernel.Agents.OpenAI;
+
+public sealed partial class OpenAIAssistantAgent : KernelAgent
+{
+    /// <summary>
+    /// Specifies a key that avoids an exception from OpenAI Client when a custom endpoint is provided without an API key.
+    /// </summary>
+    private const string SingleSpaceKey = " ";
+
+    /// <summary>
+    /// Produces an <see cref="AzureOpenAIClient"/>.
+    /// </summary>
+    /// <param name="apiKey">The API key.</param>
+    /// <param name="endpoint">The service endpoint.</param>
+    /// <param name="httpClient">A custom <see cref="HttpClient"/> for HTTP requests.</param>
+    public static AzureOpenAIClient CreateAzureOpenAIClient(ApiKeyCredential apiKey, Uri endpoint, HttpClient? httpClient = null)
+    {
+        Verify.NotNull(apiKey, nameof(apiKey));
+        Verify.NotNull(endpoint, nameof(endpoint));
+
+        AzureOpenAIClientOptions clientOptions = CreateAzureClientOptions(httpClient);
+
+        return new AzureOpenAIClient(endpoint, apiKey!, clientOptions);
+    }
+
+    /// <summary>
+    /// Produces an <see cref="AzureOpenAIClient"/>.
+    /// </summary>
+    /// <param name="credential">The credentials.</param>
+    /// <param name="endpoint">The service endpoint.</param>
+    /// <param name="httpClient">A custom <see cref="HttpClient"/> for HTTP requests.</param>
+    public static AzureOpenAIClient CreateAzureOpenAIClient(TokenCredential credential, Uri endpoint, HttpClient? httpClient = null)
+    {
+        Verify.NotNull(credential, nameof(credential));
+        Verify.NotNull(endpoint, nameof(endpoint));
+
+        AzureOpenAIClientOptions clientOptions = CreateAzureClientOptions(httpClient);
+
+        return new AzureOpenAIClient(endpoint, credential, clientOptions);
+    }
+
+    /// <summary>
+    /// Produces an <see cref="OpenAIClient"/>.
+    /// </summary>
+    /// <param name="endpoint">An optional endpoint.</param>
+    /// <param name="httpClient">A custom <see cref="HttpClient"/> for HTTP requests.</param>
+    public static OpenAIClient CreateOpenAIClient(Uri? endpoint = null, HttpClient? httpClient = null)
+    {
+        OpenAIClientOptions clientOptions = CreateOpenAIClientOptions(endpoint, httpClient);
+        return new OpenAIClient(new ApiKeyCredential(SingleSpaceKey), clientOptions);
+    }
+
+    /// <summary>
+    /// Produces an <see cref="OpenAIClient"/>.
+    /// </summary>
+    /// <param name="apiKey">The API key.</param>
+    /// <param name="endpoint">An optional endpoint.</param>
+    /// <param name="httpClient">A custom <see cref="HttpClient"/> for HTTP requests.</param>
+    public static OpenAIClient CreateOpenAIClient(ApiKeyCredential apiKey, Uri? endpoint = null, HttpClient? httpClient = null)
+    {
+        OpenAIClientOptions clientOptions = CreateOpenAIClientOptions(endpoint, httpClient);
+        return new OpenAIClient(apiKey, clientOptions);
+    }
+
+    private static AzureOpenAIClientOptions CreateAzureClientOptions(HttpClient? httpClient)
+    {
+        AzureOpenAIClientOptions options = new()
+        {
+            UserAgentApplicationId = HttpHeaderConstant.Values.UserAgent
+        };
+
+        ConfigureClientOptions(httpClient, options);
+
+        return options;
+    }
+
+    private static OpenAIClientOptions CreateOpenAIClientOptions(Uri? endpoint, HttpClient? httpClient)
+    {
+        OpenAIClientOptions options = new()
+        {
+            UserAgentApplicationId = HttpHeaderConstant.Values.UserAgent,
+            Endpoint = endpoint ?? httpClient?.BaseAddress,
+        };
+
+        ConfigureClientOptions(httpClient, options);
+
+        return options;
+    }
+
+    private static void ConfigureClientOptions(HttpClient? httpClient, ClientPipelineOptions options)
+    {
+        options.AddPolicy(CreateRequestHeaderPolicy(HttpHeaderConstant.Names.SemanticKernelVersion, HttpHeaderConstant.Values.GetAssemblyVersion(typeof(OpenAIAssistantAgent))), PipelinePosition.PerCall);
+
+        if (httpClient is not null)
+        {
+            options.Transport = new HttpClientPipelineTransport(httpClient);
+            options.RetryPolicy = new ClientRetryPolicy(maxRetries: 0); // Disable retry policy if and only if a custom HttpClient is provided.
+            options.NetworkTimeout = Timeout.InfiniteTimeSpan; // Disable default timeout
+        }
+    }
+
+    private static GenericActionPipelinePolicy CreateRequestHeaderPolicy(string headerName, string headerValue)
+        =>
+            new((message) =>
+            {
+                if (message?.Request?.Headers?.TryGetValue(headerName, out string? _) == false)
+                {
+                    message.Request.Headers.Set(headerName, headerValue);
+                }
+            });
+}

dotnet/src/Agents/OpenAI/OpenAIAssistantAgent.cs

@@ -19,7 +19,7 @@ namespace Microsoft.SemanticKernel.Agents.OpenAI;
 /// <summary>
 /// Represents a <see cref="KernelAgent"/> specialization based on Open AI Assistant / GPT.
 /// </summary>
-public sealed class OpenAIAssistantAgent : KernelAgent
+public sealed partial class OpenAIAssistantAgent : KernelAgent
 {
     /// <summary>
     /// The metadata key that identifies code-interpreter content.

dotnet/src/InternalUtilities/samples/AgentUtilities/BaseAssistantTest.cs

@@ -17,15 +17,14 @@ public abstract class BaseAssistantTest : BaseAgentsTest<OpenAIClient>
 {
     protected BaseAssistantTest(ITestOutputHelper output) : base(output)
     {
-        var clientProvider =
+        this.Client =
             this.UseOpenAIConfig ?
-                OpenAIClientProvider.ForOpenAI(new ApiKeyCredential(this.ApiKey ?? throw new ConfigurationNotFoundException("OpenAI:ApiKey"))) :
+                OpenAIAssistantAgent.CreateOpenAIClient(new ApiKeyCredential(this.ApiKey ?? throw new ConfigurationNotFoundException("OpenAI:ApiKey"))) :
                 !string.IsNullOrWhiteSpace(this.ApiKey) ?
-                    OpenAIClientProvider.ForAzureOpenAI(new ApiKeyCredential(this.ApiKey), new Uri(this.Endpoint!)) :
-                    OpenAIClientProvider.ForAzureOpenAI(new AzureCliCredential(), new Uri(this.Endpoint!));
+                    OpenAIAssistantAgent.CreateAzureOpenAIClient(new ApiKeyCredential(this.ApiKey), new Uri(this.Endpoint!)) :
+                    OpenAIAssistantAgent.CreateAzureOpenAIClient(new AzureCliCredential(), new Uri(this.Endpoint!));
 
-        this.Client = clientProvider.Client;
-        this.AssistantClient = clientProvider.AssistantClient;
+        this.AssistantClient = this.Client.GetAssistantClient();
     }
 
     /// <inheritdoc/>

dotnet/src/InternalUtilities/samples/AgentUtilities/BaseAzureTest.cs

@@ -14,10 +14,8 @@ public abstract class BaseAzureAgentTest : BaseAgentsTest<AIProjectClient>
 {
     protected BaseAzureAgentTest(ITestOutputHelper output) : base(output)
     {
-        var clientProvider = AzureAIClientProvider.FromConnectionString(TestConfiguration.AzureAI.ConnectionString, new AzureCliCredential());
-
-        this.Client = clientProvider.Client;
-        this.AgentsClient = clientProvider.AgentsClient;
+        this.Client = AzureAIAgent.CreateAzureAIClient(TestConfiguration.AzureAI.ConnectionString, new AzureCliCredential());
+        this.AgentsClient = this.Client.GetAgentsClient();
     }
 
     /// <inheritdoc/>