Supply a certificate selection callback delegate,

so the client can select the particular cert in the
collection to send to server.

If this is not done, the certificate is null, and is
never sent

Author: essiene

src/client/api/SslHelper.cs

@@ -71,11 +71,22 @@ namespace RabbitMQ.Client
     public class SslHelper
     {
 
+        static X509Certificate CertificateSelectionCallback(object sender,
+                string targetHost,
+                X509CertificateCollection localCertificates,
+                X509Certificate remoteCertificate,
+                string[] acceptableIssuers)
+        {
+            return localCertificates[0];
+        }
+
         ///<summary>Upgrade a Tcp stream to an Ssl stream using the SSL options
         ///provided</summary>
         public static Stream TcpUpgrade(Stream tcpStream, SslOption sslOption)
         {
-            SslStream sslStream = new SslStream(tcpStream, false);
+            SslStream sslStream = new SslStream(tcpStream, false,
+                    null,
+                    new LocalCertificateSelectionCallback(CertificateSelectionCallback));
 
             sslStream.AuthenticateAsClient(sslOption.ServerName,
                         sslOption.Certs,