Xamarin Android - Call API using HttpClient with Certificate

Finally managed to get it work :D For those who are interested, here's how I achieve it :

TL;DR: Upgrade to Visual Studio 2019 and HttpWebRequest comes to the rescue (you can find the code sample below) ;-)

Context: our project consists of a PCL and a Android project. In the team, we know we have to migrate the PCL to a .NET Standard project but it takes time, especially when you have a lot of librairies to deal with (libraries that are not updated to .NET Standard) xP

• When you want to call an API, the first thing that comes to your mind is to use the HttpClient/HttpRequestHandler pair where we just have to pass our certificate in the HttpRequestHandler as follows :

  httpRequestHandler.ClientCertificates.Add(new X509Certificate2(..))

Why it didn't work ? Because we're developing with Xamarin.Android which uses under the hood Mono.Droid, therefore we're meeting the unpopular NotImplementedException() ! What about WebRequestHandler ? Well the same fate :P

Hopefully the salvation came from HttpWebRequest as follows :

        private Task<string> ExecuteRequest(Uri uri, X509Certificate2 certificate)
        {
            // Create a web request that points to our secured Backend API
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(uri);

            if (certificate != null)
            {
                // Associate the certificates with the request
                request.ClientCertificates.Add(certificate);
            }

            // Launch the web request
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            // Output the stream to a jsonTextReader or anything else depending on your needs
            using (Stream stream = response.GetResponseStream())
            using (StreamReader sr = new StreamReader(stream))
            using (var jsonTextReader = new JsonTextReader(sr))
            {
                // Do whatever you want
            }
        }

This code worked on my machine (Visual Studio 2019) but not on my colleague (Visual Studio 2017) : indeed the following exception was met :

System.Security.Authentication.AuthenticationException: A call to SSPI failed, see inner exception.

I also have VS2017 installed on my machine so I've tried to execute the same code with it and as strange as it sounds, I also got the error

Et voilà :) Of course, the certificate had to be "an Embedded resource"