I am developing an ASP.NET web application that sends a request to another server using HttpWebRequest. It sends the request over HTTPS, and the remote server requires a client certificate. The request fails in the .NET application, apparently unable to send the correct client certificate. I am able to successfully connect and send the client certificate if I simply visit the url with a web browser (Chrome specifically).

The code below is a simple reproduction, with just a basic GET request.

var r = WebRequest.Create(url) as HttpWebRequest;
r.ClientCertificates = new X509CertificateCollection { myX509Cert };
using (var resp = r.GetResponse() as HttpWebResponse) {
    ...
}

I get our favorite exception, "Could not create SSL/TLS secure channel". Typically, these types of problems point to issues with permissions on your certificate's private key. I tried everything I could think of to ensure this is all configured correctly, but perhaps I missed something. Long story short, the remote server is sending a TLS CertificateRequest with a list that that does seem to properly identify my client certificate, but my appliation fails to respond with any client certificate.

Here is my setup:

  • Windows 7 professional 64 bit
  • Able to reproduce the problem in an ASP.NET MVC 3 / .NET 4 application running in the Visual Studio dev server, ASP.NET WebForms / .NET 3.5 application running in local IIS, and in a .NET console application / .NET 4
  • Microsoft .NET Framework 4.5 was recently installed. Haven't examined yet whether this could be a problem

Here is everything I've tried, and what I know:

  • This code seemed to work fine when running on a Windows XP machine
  • I ensured that my client certificate is imported into the Local Computer, Personal Certificates store, with the Private Key permissions properly configured for myself and all relevant
.net client certificate ssl
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