add support for https proxy

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs

@@ -114,6 +114,7 @@ internal sealed class HttpConnectionPool : IDisposable
         private readonly SslClientAuthenticationOptions? _sslOptionsHttp2;
         private readonly SslClientAuthenticationOptions? _sslOptionsHttp2Only;
         private SslClientAuthenticationOptions? _sslOptionsHttp3;
+        private SslClientAuthenticationOptions? _sslOptionsProxy;
 
         /// <summary>Whether the pool has been used since the last time a cleanup occurred.</summary>
         private bool _usedSinceLastCleanup = true;
@@ -302,6 +303,12 @@ public HttpConnectionPool(HttpConnectionPoolManager poolManager, HttpConnectionK
                 _http2RequestQueue = new RequestQueue<Http2Connection?>();
             }
 
+            if (_proxyUri != null && HttpUtilities.IsSupportedSecureScheme(_proxyUri.Scheme))
+            {
+                _sslOptionsProxy = ConstructSslOptions(poolManager, _proxyUri.IdnHost);
+                _sslOptionsProxy.ApplicationProtocols = null;
+            }
+
             if (NetEventSource.Log.IsEnabled()) Trace($"{this}");
         }
 
@@ -1525,10 +1532,18 @@ public ValueTask<HttpResponseMessage> SendAsync(HttpRequestMessage request, bool
                 case HttpConnectionKind.ProxyConnect:
                     Debug.Assert(_originAuthority != null);
                     stream = await ConnectToTcpHostAsync(_originAuthority.IdnHost, _originAuthority.Port, request, async, cancellationToken).ConfigureAwait(false);
+                    if (_kind == HttpConnectionKind.ProxyConnect && _sslOptionsProxy != null)
+                    {
+                        stream = await ConnectHelper.EstablishSslConnectionAsync(_sslOptionsProxy, request, async, stream, cancellationToken).ConfigureAwait(false);
+                    }
                     break;
 
                 case HttpConnectionKind.Proxy:
                     stream = await ConnectToTcpHostAsync(_proxyUri!.IdnHost, _proxyUri.Port, request, async, cancellationToken).ConfigureAwait(false);
+                    if (_sslOptionsProxy != null)
+                    {
+                        stream = await ConnectHelper.EstablishSslConnectionAsync(_sslOptionsProxy, request, async, stream, cancellationToken).ConfigureAwait(false);
+                    }
                     break;
 
                 case HttpConnectionKind.ProxyTunnel:

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs

@@ -25,7 +25,7 @@ namespace System.Net.Http
     // (8) HttpConnection.SendAsyncCore: Write request to connection and read response
     //                                   Also, handle cookie processing
     //
-    // Redirect and deompression handling are done above HttpConnectionPoolManager,
+    // Redirect and decompression handling are done above HttpConnectionPoolManager,
     // in RedirectHandler and DecompressionHandler respectively.
 
     /// <summary>Provides a set of connection pools, each for its own endpoint.</summary>

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpEnvironmentProxy.cs

@@ -128,11 +128,18 @@ private HttpEnvironmentProxy(Uri? httpProxy, Uri? httpsProxy, string? bypassList
 
             int hostIndex = 0;
             string protocol = "http";
+            ushort port = 80;
 
             if (value.StartsWith("http://", StringComparison.OrdinalIgnoreCase))
             {
                 hostIndex = 7;
             }
+            else if (value.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
+            {
+                hostIndex = 8;
+                protocol = "https";
+                port = 443;
+            }
             else if (value.StartsWith("socks4://", StringComparison.OrdinalIgnoreCase))
             {
                 hostIndex = 9;
@@ -156,7 +163,6 @@ private HttpEnvironmentProxy(Uri? httpProxy, Uri? httpsProxy, string? bypassList
 
             string? user = null;
             string? password = null;
-            ushort port = 80;
             string host;
 
             // Check if there is authentication part with user and possibly password.

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpUtilities.cs

@@ -22,7 +22,7 @@ internal static bool IsSecureWebSocketScheme(string scheme) =>
             string.Equals(scheme, "wss", StringComparison.OrdinalIgnoreCase);
 
         internal static bool IsSupportedProxyScheme(string scheme) =>
-            string.Equals(scheme, "http", StringComparison.OrdinalIgnoreCase) || IsSocksScheme(scheme);
+            string.Equals(scheme, "http", StringComparison.OrdinalIgnoreCase) || string.Equals(scheme, "https", StringComparison.OrdinalIgnoreCase) || IsSocksScheme(scheme);
 
         internal static bool IsSocksScheme(string scheme) =>
             string.Equals(scheme, "socks5", StringComparison.OrdinalIgnoreCase) ||

src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs

@@ -7,13 +7,11 @@
 using System.IO.Pipes;
 using System.Linq;
 using System.Net.Http.Headers;
-using System.Net.Quic;
 using System.Net.Security;
 using System.Net.Sockets;
 using System.Net.Test.Common;
 using System.Numerics;
 using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 using System.Security.Authentication;
 using System.Security.Cryptography.X509Certificates;
 using System.Text;
@@ -656,6 +654,45 @@ public SocketsHttpHandler_HttpClientHandler_SslProtocols_Test(ITestOutputHelper
     public sealed class SocketsHttpHandler_HttpClientHandler_Proxy_Test : HttpClientHandler_Proxy_Test
     {
         public SocketsHttpHandler_HttpClientHandler_Proxy_Test(ITestOutputHelper output) : base(output) { }
+
+        [Theory]
+        [InlineData(true)]
+        [InlineData(false)]
+        public async Task Proxy_Https_Succeeds(bool secureUri)
+        {
+            var releaseServer = new TaskCompletionSource();
+            await LoopbackServer.CreateClientAndServerAsync(async uri =>
+            {
+                bool validationCalled = false;
+                using SocketsHttpHandler handler = CreateSocketsHttpHandler(allowAllCertificates: true);
+
+                handler.Proxy = new UseSpecifiedUriWebProxy(uri, new NetworkCredential("abc", "password"));
+                handler.SslOptions.RemoteCertificateValidationCallback = (sender, certificate, chain, error) =>
+                {
+                    validationCalled = true;
+                    return true;
+                };
+
+                using (HttpClient client = CreateHttpClient(handler))
+                {
+                    HttpResponseMessage response = await client.GetAsync(secureUri ? "https://foo.bar/" : "http://foo.bar/");
+                    Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+                    Assert.True(validationCalled);
+
+                }
+            }, server => server.AcceptConnectionAsync(async connection =>
+            {
+                await connection.ReadRequestHeaderAndSendResponseAsync();
+                if (secureUri)
+                {
+                    // client will send CONNECT and if that succeeds it will negotiate TLS
+
+                    var sslConnection = await LoopbackServer.Connection.CreateAsync(null, connection.Stream, new LoopbackServer.Options { UseSsl = true });
+                    await sslConnection.ReadRequestHeaderAndSendResponseAsync();
+                }
+            }),
+            new LoopbackServer.Options { UseSsl = true });
+        }
     }
 
     public abstract class SocketsHttpHandler_TrailingHeaders_Test : HttpClientHandlerTestBase

src/libraries/System.Net.Http/tests/UnitTests/HttpEnvironmentProxyTest.cs

@@ -142,6 +142,8 @@ public void HttpProxy_EnvironmentProxy_Loaded()
         [InlineData("socks4://1.2.3.4:8888/foo", "1.2.3.4", "8888", null, null)]
         [InlineData("socks4a://1.2.3.4:8888/foo", "1.2.3.4", "8888", null, null)]
         [InlineData("socks5://1.2.3.4:8888/foo", "1.2.3.4", "8888", null, null)]
+        [InlineData("https://1.1.1.5:3005", "1.1.1.5", "3005", null, null)]
+        [InlineData("https://1.1.1.5", "1.1.1.5", "443", null, null)]
         public void HttpProxy_Uri_Parsing(string _input, string _host, string _port, string _user, string _password)
         {
             RemoteExecutor.Invoke((input, host, port, user, password) =>