.Net: AddOpenAIEmbeddingGenerator now respects HttpClient.BaseAddress for endpoint. (#12810)

### Description

This PR fixes an issue where AddOpenAIEmbeddingGenerator() ignored the
BaseAddress of the provided HttpClient, always using the default OpenAI
endpoint. Now, if a custom BaseAddress is set on the HttpClient, it is
passed as the endpoint parameter, ensuring requests are sent to the
correct server. This aligns the behavior with other OpenAI service
registrations and enables proxy or custom endpoint scenarios.

FIxes #12806

---------

Co-authored-by: Adit Sheth <[email protected]>
Co-authored-by: Roger Barreto <[email protected]>
Co-authored-by: SergeyMenshykh <[email protected]>

Author: 4 people

dotnet/src/Connectors/Connectors.OpenAI.UnitTests/Extensions/KernelBuilderExtensionsTests.cs

@@ -144,6 +144,24 @@ public void ItCanAddAudioToTextServiceWithOpenAIClient()
         Assert.Equal("model", service.Attributes[AIServiceExtensions.ModelIdKey]);
     }
 
+    [Fact]
+    public void ItCanAddEmbeddingGeneratorWithHttpClient()
+    {
+        // Arrange
+        var customEndpoint = new Uri("https://custom.proxy.url/openai/v1/");
+        using var httpClient = new System.Net.Http.HttpClient { BaseAddress = customEndpoint };
+        var sut = Kernel.CreateBuilder();
+
+        // Act
+        var kernel = sut.AddOpenAIEmbeddingGenerator("model", "key", httpClient: httpClient)
+            .Build();
+        var service = kernel.GetRequiredService<IEmbeddingGenerator<string, Embedding<float>>>();
+
+        // Assert
+        Assert.NotNull(service);
+        Assert.Equal(customEndpoint, service.GetService<EmbeddingGeneratorMetadata>()!.ProviderUri);
+    }
+
     [Fact]
     [Obsolete(ObsoleteMessage)]
     public void ItCanAddFileService()

dotnet/src/Connectors/Connectors.OpenAI/Core/ClientCore.cs

@@ -199,10 +199,7 @@ internal static OpenAIClientOptions GetOpenAIClientOptions(HttpClient? httpClien
             UserAgentApplicationId = HttpHeaderConstant.Values.UserAgent,
         };
 
-        if (endpoint is not null)
-        {
-            options.Endpoint = endpoint;
-        }
+        options.Endpoint ??= endpoint ?? httpClient?.BaseAddress;
 
         options.AddPolicy(CreateRequestHeaderPolicy(HttpHeaderConstant.Names.SemanticKernelVersion, HttpHeaderConstant.Values.GetAssemblyVersion(typeof(ClientCore))), PipelinePosition.PerCall);
 

dotnet/src/Connectors/Connectors.OpenAI/Extensions/OpenAIServiceCollectionExtensions.DependencyInjection.cs

@@ -2,7 +2,6 @@
 
 using System;
 using System.ClientModel;
-using System.ClientModel.Primitives;
 using System.Diagnostics.CodeAnalysis;
 using System.Net.Http;
 using Microsoft.Extensions.AI;
@@ -275,29 +274,4 @@ public static IServiceCollection AddOpenAIEmbeddingGenerator(this IServiceCollec
         });
     }
     #endregion
-
-    private static OpenAIClientOptions GetClientOptions(
-        Uri? endpoint = null,
-        string? orgId = null,
-        HttpClient? httpClient = null)
-    {
-        OpenAIClientOptions options = new();
-
-        if (endpoint is not null)
-        {
-            options.Endpoint = endpoint;
-        }
-
-        if (orgId is not null)
-        {
-            options.OrganizationId = orgId;
-        }
-
-        if (httpClient is not null)
-        {
-            options.Transport = new HttpClientPipelineTransport(httpClient);
-        }
-
-        return options;
-    }
 }