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HttpClient Sending X509 Certificate

Hey Everyone,

I am working on a Xamarin Forms project that needs to send out a Http request that includes a certificate for authentication.

I have the code working to get the certificate, which is a PFX, and pass it to my HttpClient but when I make the request I always get back a 403 error. The code below is how I am sending the message:

// Attach certifcate collection to handler.
 var handler = new HttpClientHandler();
 handler.ClientCertificateOptions = ClientCertificateOption.Manual;

 // Construct client with handler.
var client = new HttpClient(handler);

// Make request.
var result = client.GetAsync("urlgoeshere").GetAwaiter().GetResult();
var responsebody = result.Content.ReadAsStringAsync().GetAwaiter().GetResult();

I removed the real URL, but with the correct one it is always a 403 error.

I then tested this with a HttpWebRequest and I get through just fine, the code for that is as follows:

X509Certificate2Collection certificate = GetCertificate();
var httpRequest = (HttpWebRequest)WebRequest.Create("urlgoeshere");
httpRequest.ClientCertificates = certificate;
HttpWebResponse response = (HttpWebResponse)httpRequest.GetResponse();

So I am curious if anyone has seen this before and if they have what the difference is? And how you could get this fixed to work with the HttpClient?


  • ColeXColeX Member, Xamarin Team Xamurai
    edited August 2020

    Try the following code

        var certHandler = new HttpClientHandler();
        certHandler.ClientCertificateOptions = ClientCertificateOption.Manual;            
        certHandler.UseDefaultCredentials = false;
        var certificate = new X509Certificate2(Properties.Resources.SigningCert, "password", X509KeyStorageFlags.UserKeySet); //Must be renewed and replaced every year.
        //Execute the command            
        var client = new HttpClient(certHandler);
        string result;
            result = await client.GetStringAsync(url);
        catch (Exception ex)
            throw ex;

    Refer to .

  • akemper1akemper1 Member ✭✭
    edited August 2020

    Hey ColeX,

    I have tried this and with no luck, I think I have found the answer though. I believe Mono.Droid (which Xamarin.Android uses) which HttpClient will go to just does not implement the Handler.ClientCertificates, so the certificate is actually not sent with the request.

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