From e1a22b315dae5fc1335114908a545cd706af6c60 Mon Sep 17 00:00:00 2001
From: James Newton-King <james@newtonking.com>
Date: Thu, 17 May 2018 06:25:40 +1200
Subject: [PATCH] Android HttpClientHandler.ClientCertificates fix (#2270)

---
 .../HttpConnection.cs                                  | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Http.Connections.Client/HttpConnection.cs b/src/Microsoft.AspNetCore.Http.Connections.Client/HttpConnection.cs
index 176554485f..ae0af781ec 100644
--- a/src/Microsoft.AspNetCore.Http.Connections.Client/HttpConnection.cs
+++ b/src/Microsoft.AspNetCore.Http.Connections.Client/HttpConnection.cs
@@ -486,10 +486,16 @@ namespace Microsoft.AspNetCore.Http.Connections.Client
                 {
                     httpClientHandler.CookieContainer = _httpConnectionOptions.Cookies;
                 }
-                if (_httpConnectionOptions.ClientCertificates != null)
+
+                // Only access HttpClientHandler.ClientCertificates if the user has configured client certs
+                // Mono does not support client certs and will throw NotImplementedException
+                // https://github.com/aspnet/SignalR/issues/2232
+                var clientCertificates = _httpConnectionOptions.ClientCertificates;
+                if (clientCertificates?.Count > 0)
                 {
-                    httpClientHandler.ClientCertificates.AddRange(_httpConnectionOptions.ClientCertificates);
+                    httpClientHandler.ClientCertificates.AddRange(clientCertificates);
                 }
+
                 if (_httpConnectionOptions.UseDefaultCredentials != null)
                 {
                     httpClientHandler.UseDefaultCredentials = _httpConnectionOptions.UseDefaultCredentials.Value;