Most flexibility provides gRPC connection

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/.publicApi/Stable/net6.0/PublicAPI.Shipped.txt

@@ -9,6 +9,8 @@ OpenTelemetry.Exporter.OtlpExporterOptions.Headers.get -> string
 OpenTelemetry.Exporter.OtlpExporterOptions.Headers.set -> void
 OpenTelemetry.Exporter.OtlpExporterOptions.HttpClientFactory.get -> System.Func<System.Net.Http.HttpClient>
 OpenTelemetry.Exporter.OtlpExporterOptions.HttpClientFactory.set -> void
+OpenTelemetry.Exporter.OtlpExporterOptions.HttpHandlerFactory.get -> System.Func<System.Net.Http.HttpMessageHandler>
+OpenTelemetry.Exporter.OtlpExporterOptions.HttpHandlerFactory.set -> void
 OpenTelemetry.Exporter.OtlpExporterOptions.OtlpExporterOptions() -> void
 OpenTelemetry.Exporter.OtlpExporterOptions.Protocol.get -> OpenTelemetry.Exporter.OtlpExportProtocol
 OpenTelemetry.Exporter.OtlpExporterOptions.Protocol.set -> void

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/.publicApi/Stable/netstandard2.1/PublicAPI.Shipped.txt

@@ -9,6 +9,8 @@ OpenTelemetry.Exporter.OtlpExporterOptions.Headers.get -> string
 OpenTelemetry.Exporter.OtlpExporterOptions.Headers.set -> void
 OpenTelemetry.Exporter.OtlpExporterOptions.HttpClientFactory.get -> System.Func<System.Net.Http.HttpClient>
 OpenTelemetry.Exporter.OtlpExporterOptions.HttpClientFactory.set -> void
+OpenTelemetry.Exporter.OtlpExporterOptions.HttpHandlerFactory.get -> System.Func<System.Net.Http.HttpMessageHandler>
+OpenTelemetry.Exporter.OtlpExporterOptions.HttpHandlerFactory.set -> void
 OpenTelemetry.Exporter.OtlpExporterOptions.OtlpExporterOptions() -> void
 OpenTelemetry.Exporter.OtlpExporterOptions.Protocol.get -> OpenTelemetry.Exporter.OtlpExportProtocol
 OpenTelemetry.Exporter.OtlpExporterOptions.Protocol.set -> void

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+* GrpcExporter support custom HttpClient.
+  ([#4813](https://github.com/open-telemetry/opentelemetry-dotnet/pull/4815))
+
 ## 1.6.0
 
 Released 2023-Sep-05

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/OtlpExporterOptions.cs

@@ -192,6 +192,41 @@ public Uri Endpoint
     /// </remarks>
     public Func<HttpClient> HttpClientFactory { get; set; }
 
+#if NETSTANDARD2_1 || NET6_0_OR_GREATER
+    /// <summary>
+    /// Gets or sets the factory function called to create the <see
+    /// cref="HttpMessageHandler"/> instance that will be used at runtime to
+    /// transmit telemetry over HTTP. The returned instance will be reused
+    /// for all export invocations.
+    /// </summary>
+    /// <remarks>
+    /// Notes:
+    /// <list type="bullet">
+    /// <item>This is only invoked for the <see
+    /// cref="OtlpExportProtocol.Grpc"/> protocol.</item>
+    /// <item>The default behavior when using the <see
+    /// cref="OtlpTraceExporterHelperExtensions.AddOtlpExporter(TracerProviderBuilder,
+    /// Action{OtlpExporterOptions})"/> extension is if an <a
+    /// href="https://docs.microsoft.com/dotnet/api/system.net.http.ihttpmessagehandlerfactory">IHttpMessageHandlerFactory</a>
+    /// instance can be resolved through the application <see
+    /// cref="IServiceProvider"/> then an <see cref="HttpMessageHandler"/> will be
+    /// created through the factory with the name "OtlpTraceExporter"
+    /// otherwise an <see cref="HttpMessageHandler"/> will be instantiated
+    /// directly.</item>
+    /// <item>The default behavior when using the <see
+    /// cref="OtlpMetricExporterExtensions.AddOtlpExporter(MeterProviderBuilder,
+    /// Action{OtlpExporterOptions})"/> extension is if an <a
+    /// href="https://docs.microsoft.com/dotnet/api/system.net.http.ihttpmessagehandlerfactory">IHttpMessageHandlerFactory</a>
+    /// instance can be resolved through the application <see
+    /// cref="IServiceProvider"/> then an <see cref="HttpMessageHandler"/> will be
+    /// created through the factory with the name "OtlpMetricExporter"
+    /// otherwise an <see cref="HttpMessageHandler"/> will be instantiated
+    /// directly.</item>
+    /// </list>
+    /// </remarks>
+    public Func<HttpMessageHandler> HttpHandlerFactory { get; set; }
+#endif
+
     /// <summary>
     /// Gets a value indicating whether <see cref="Endpoint" /> was modified via its setter.
     /// </summary>

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/OtlpExporterOptionsExtensions.cs

@@ -43,7 +43,7 @@ public static Channel CreateChannel(this OtlpExporterOptions options)
         }
 
 #if NETSTANDARD2_1 || NET6_0_OR_GREATER
-        return GrpcChannel.ForAddress(options.Endpoint);
+        return GrpcChannel.ForAddress(options.Endpoint, new GrpcChannelOptions { HttpHandler = options.HttpHandlerFactory?.Invoke() });
 #else
         ChannelCredentials channelCredentials;
         if (options.Endpoint.Scheme == Uri.UriSchemeHttps)

test/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests/Implementation/ExportClient/OtlpGrpcTraceExportClientTests.cs

@@ -0,0 +1,87 @@
+// <copyright file="OtlpGrpcTraceExportClientTests.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+#if NET6_0_OR_GREATER
+using System.Reflection;
+using Grpc.Net.Client;
+using Moq;
+#endif
+using OpenTelemetry.Exporter.OpenTelemetryProtocol.Implementation.ExportClient;
+using Xunit;
+
+namespace OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests;
+
+public class OtlpGrpcTraceExportClientTests
+{
+    [Fact]
+    public void NewOtlpGrpcTraceExportClient_OtlpExporterOptions_ExporterHasCorrectProperties()
+    {
+        var header1 = new
+        {
+            Name = "hdr1",
+            Value = "val1"
+        };
+        var header2 = new
+        {
+            Name = "hdr2",
+            Value = "val2"
+        };
+
+        var options = new OtlpExporterOptions
+        {
+            Headers = $"{header1.Name}={header1.Value}, {header2.Name} = {header2.Value}",
+        };
+
+        var client = new OtlpGrpcTraceExportClient(options);
+
+        Assert.NotNull(client.Channel);
+
+        Assert.Equal(2 + OtlpExporterOptions.StandardHeaders.Length, client.Headers.Count);
+        Assert.Contains(client.Headers, kvp => kvp.Key == header1.Name && kvp.Value == header1.Value);
+        Assert.Contains(client.Headers, kvp => kvp.Key == header2.Name && kvp.Value == header2.Value);
+
+        for (int i = 0; i < OtlpExporterOptions.StandardHeaders.Length; i++)
+        {
+            Assert.Contains(client.Headers, entry => entry.Key.Equals(OtlpExporterOptions.StandardHeaders[i].Key, StringComparison.OrdinalIgnoreCase) && entry.Value == OtlpExporterOptions.StandardHeaders[i].Value);
+        }
+    }
+
+#if NET6_0_OR_GREATER
+    [Fact]
+    public void NewOtlpGrpcTraceExportClient_UseCustomHttpClient()
+    {
+        var httpHandler = new Mock<HttpMessageHandler>();
+
+        var options = new OtlpExporterOptions
+        {
+            HttpHandlerFactory = () => httpHandler.Object
+        };
+
+        var client = new OtlpGrpcTraceExportClient(options);
+
+        var httpInvoker = Assert.IsAssignableFrom<HttpMessageInvoker>(typeof(GrpcChannel).GetProperty("HttpInvoker", BindingFlags.Instance | BindingFlags.NonPublic)?.GetValue(client.Channel));
+
+        var httpMessageHandler = Assert.IsAssignableFrom<HttpMessageHandler>(typeof(HttpMessageInvoker).GetField("_handler", BindingFlags.Instance | BindingFlags.NonPublic)?.GetValue(httpInvoker));
+
+        while (httpMessageHandler is DelegatingHandler delegatingHandler)
+        {
+            httpMessageHandler = delegatingHandler.InnerHandler;
+        }
+
+        Assert.Equal(httpHandler.Object, httpMessageHandler);
+    }
+#endif
+}