Wrap CurlHandler cert validation callback exceptions in HttpRequestException

src/System.Net.Http/src/System/Net/Http/Unix/CurlException.cs

@@ -13,6 +13,11 @@ internal CurlException(int error, string message) : base(message)
             HResult = error;
         }
 
+        internal CurlException(int error, Exception innerException) : base(GetCurlErrorString(error, isMulti:false), innerException)
+        {
+            HResult = error;
+        }
+
         internal CurlException(int error, bool isMulti) : this(error, GetCurlErrorString(error, isMulti))
         {
         }

src/System.Net.Http/src/System/Net/Http/Unix/CurlHandler.SslProvider.cs

@@ -266,7 +266,7 @@ private static int VerifyCertChain(IntPtr storeCtxPtr, IntPtr curlPtr)
                 catch (Exception exc)
                 {
                     EventSourceTrace("Unexpected exception: {0}", exc, easy: easy);
-                    easy.FailRequest(exc);
+                    easy.FailRequest(CreateHttpRequestException(new CurlException((int)CURLcode.CURLE_ABORTED_BY_CALLBACK, exc)));
                     return FailureResult;
                 }
                 finally

src/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.ServerCertificates.cs

@@ -162,6 +162,7 @@ public async Task UseCallback_CallbackReturnsFailure_ThrowsException()
             }
         }
 
+        [ActiveIssue(21904)]
         [OuterLoop] // TODO: Issue #11345
         [Fact]
         public async Task UseCallback_CallbackThrowsException_ExceptionPropagates()