diff --git a/.gitignore b/.gitignore
index f5dc20d..ac2791b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@ build/
 *.userprefs
 build/
 *.xam
+*.suo
\ No newline at end of file
diff --git a/src/ModernHttpClient/Android/OkHttpNetworkHandler.cs b/src/ModernHttpClient/Android/OkHttpNetworkHandler.cs
index de6d3c3..3355afa 100644
--- a/src/ModernHttpClient/Android/OkHttpNetworkHandler.cs
+++ b/src/ModernHttpClient/Android/OkHttpNetworkHandler.cs
@@ -13,6 +13,11 @@
 using System.Globalization;
 using Android.OS;
 
+// See http://chariotsolutions.com/blog/post/https-with-client-certificates-on/
+// for clue on Android client certs http://square.github.io/okhttp/javadoc/com/squareup/okhttp/CertificatePinner.html
+using Java.Security;
+
+
 namespace ModernHttpClient
 {
     public class NativeMessageHandler : HttpClientHandler
@@ -32,12 +37,44 @@ public class NativeMessageHandler : HttpClientHandler
 
         public NativeMessageHandler() : this(false, false) {}
 
-        public NativeMessageHandler(bool throwOnCaptiveNetwork, bool customSSLVerification, NativeCookieHandler cookieHandler = null)
+        public NativeMessageHandler(
+            bool throwOnCaptiveNetwork, bool customSSLVerification, 
+            NativeCookieHandler cookieHandler = null,
+            byte[] pfxData = null, string pfxPassword = null)
         {
             this.throwOnCaptiveNetwork = throwOnCaptiveNetwork;
 
             if (customSSLVerification) client.SetHostnameVerifier(new HostnameVerifier());
             noCacheCacheControl = (new CacheControl.Builder()).NoCache().Build();
+
+            if (pfxData != null && pfxData.Length > 0) {
+                var sslSocketFactory = createSSLSocketFactory(pfxData, pfxPassword);
+                client.SetSslSocketFactory(sslSocketFactory);
+            }
+        }
+            
+        private SSLSocketFactory createSSLSocketFactory(byte[] pfxData, string pfxPassword)
+        {     
+            var sslSocketFactory = client.SslSocketFactory;
+
+            try {
+                var stream = new System.IO.MemoryStream(pfxData);     
+                KeyStore keyStore = KeyStore.GetInstance("PKCS12");
+                keyStore.Load(stream, pfxPassword.ToCharArray());
+
+                KeyManagerFactory kmf = KeyManagerFactory.GetInstance("X509");
+                kmf.Init(keyStore, pfxPassword.ToCharArray());
+                IKeyManager[] keyManagers = kmf.GetKeyManagers();
+
+                SSLContext sslContext = SSLContext.GetInstance("TLS");
+                sslContext.Init(keyManagers, null, null);
+                sslSocketFactory = sslContext.SocketFactory;
+
+            } catch (Exception e) {
+                throw e; // The system has no TLS. Just give up.
+            }
+
+            return sslSocketFactory;
         }
 
         public void RegisterForProgress(HttpRequestMessage request, ProgressDelegate callback)
diff --git a/src/ModernHttpClient/ModernHttpClient.Android.csproj b/src/ModernHttpClient/ModernHttpClient.Android.csproj
index 87271cd..52a5524 100644
--- a/src/ModernHttpClient/ModernHttpClient.Android.csproj
+++ b/src/ModernHttpClient/ModernHttpClient.Android.csproj
@@ -15,7 +15,6 @@
     <MonoAndroidAssetsPrefix>Assets</MonoAndroidAssetsPrefix>
     <AndroidUseLatestPlatformSdk>False</AndroidUseLatestPlatformSdk>
     <AssemblyName>ModernHttpClient</AssemblyName>
-    <TargetFrameworkVersion>v2.3</TargetFrameworkVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>
diff --git a/src/ModernHttpClient/iOS/NSUrlSessionHandler.cs b/src/ModernHttpClient/iOS/NSUrlSessionHandler.cs
index 7226c51..78d59dd 100644
--- a/src/ModernHttpClient/iOS/NSUrlSessionHandler.cs
+++ b/src/ModernHttpClient/iOS/NSUrlSessionHandler.cs
@@ -11,11 +11,14 @@
 using System.Text.RegularExpressions;
 using ModernHttpClient.CoreFoundation;
 using ModernHttpClient.Foundation;
+using System.Security;
 
 #if UNIFIED
 using Foundation;
+using Security;
 #else
 using MonoTouch.Foundation;
+using MonoTouch.Security;
 using System.Globalization;
 #endif
 
@@ -52,11 +55,14 @@ public class NativeMessageHandler : HttpClientHandler
         public bool DisableCaching { get; set; }
 
         public NativeMessageHandler(): this(false, false) { }
-        public NativeMessageHandler(bool throwOnCaptiveNetwork, bool customSSLVerification, NativeCookieHandler cookieHandler = null)
+        public NativeMessageHandler(
+            bool throwOnCaptiveNetwork, bool customSSLVerification, 
+            NativeCookieHandler cookieHandler = null,
+            byte[] pfxData = null, string pfxPassword = null)
         {
             session = NSUrlSession.FromConfiguration(
                 NSUrlSessionConfiguration.DefaultSessionConfiguration, 
-                new DataTaskDelegate(this), null);
+                new DataTaskDelegate(this, pfxData, pfxPassword), null);
 
             this.throwOnCaptiveNetwork = throwOnCaptiveNetwork;
             this.customSSLVerification = customSSLVerification;
@@ -142,10 +148,16 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
         class DataTaskDelegate : NSUrlSessionDataDelegate
         {
             NativeMessageHandler This { get; set; }
+            NSUrlCredential _credential;
 
-            public DataTaskDelegate(NativeMessageHandler that)
+            public DataTaskDelegate(NativeMessageHandler that, byte[] pfxData = null, string pfxPassword = null)
             {
                 this.This = that;
+
+                if (pfxData != null)
+                {
+                    _credential = exportCredential(pfxData, pfxPassword);
+                }
             }
 
             public override void DidReceiveResponse(NSUrlSession session, NSUrlSessionDataTask dataTask, NSUrlResponse response, Action<NSUrlSessionResponseDisposition> completionHandler)
@@ -242,16 +254,71 @@ InflightOperation getResponseForTask(NSUrlSessionTask task)
 
             static readonly Regex cnRegex = new Regex(@"CN\s*=\s*([^,]*)", RegexOptions.Compiled | RegexOptions.CultureInvariant | RegexOptions.Singleline);
 
+            private static NSUrlCredential exportCredential(byte[] pfxData, string password = null)
+            {
+                NSDictionary[] items;
+                NSDictionary opt;
+
+                if (String.IsNullOrEmpty(password)) {
+                    opt = new NSDictionary();
+                } else {
+                    opt = NSDictionary.FromObjectsAndKeys(
+                        new object[] { password }, new object[] { "passphrase" });
+                }
+
+                var status = SecImportExport.ImportPkcs12(pfxData, opt, out items);
+
+                if (status == SecStatusCode.Success)
+                {
+                    var identityRef = items[0]["identity"];
+
+                    var identity = new SecIdentity(identityRef.Handle);
+
+                    SecCertificate[] certs = { identity.Certificate };
+
+                    var credential = new NSUrlCredential(identity, certs, NSUrlCredentialPersistence.ForSession);
+                    return credential;
+                }
+                
+                return null;
+            }
+
             public override void DidReceiveChallenge(NSUrlSession session, NSUrlSessionTask task, NSUrlAuthenticationChallenge challenge, Action<NSUrlSessionAuthChallengeDisposition, NSUrlCredential> completionHandler)
             {
                 if (!This.customSSLVerification) {
                     goto doDefault;
                 }
 
-                if (challenge.ProtectionSpace.AuthenticationMethod != "NSURLAuthenticationMethodServerTrust") {
-                    goto doDefault;
+                // https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/URLLoadingSystem/Articles/AuthenticationChallenges.html\
+                // For Client Certificate,  
+                //      http://stackoverflow.com/questions/21537203/ios-nsurlauthenticationmethodclientcertificate-not-requested-vs-activesync-serve
+                //      http://www.sunethmendis.com/2013/01/11/certificate-based-client-authentication-in-ios/
+                //      https://forums.xamarin.com/discussion/39535/didreceivechallenge-issue-with-x509-certificates
+                switch (challenge.ProtectionSpace.AuthenticationMethod)
+                {
+                    case "NSURLAuthenticationMethodServerTrust":
+                        goto serverTrust;
+                    case "NSURLAuthenticationMethodClientCertificate":
+                        goto clientCert;
+                    case "NSURLAuthenticationMethodHTTPBasic":
+                    case "NSURLAuthenticationMethodHTTPDigest":
+                    case "NSURLAuthenticationMethodNTLM":
+                    default:
+                        goto doDefault;
                 }
 
+            clientCert:
+                if (_credential == null)
+                    goto doDefault;
+
+#if UNIFIED
+                challenge.Sender.UseCredential(_credential, challenge);
+#else
+                challenge.Sender.UseCredentials(_credential, challenge);
+#endif
+                goto doDefault;
+
+            serverTrust:
                 if (ServicePointManager.ServerCertificateValidationCallback == null) {
                     goto doDefault;
                 }