WCF client behind corporate proxy authentication failure

https://github.com/dotnet/wcf/issues/3311

I'm running into an issue when calling an external WCF behind a corporate proxy. In full .Net framework the following was placed in the app.config file which allowed the call to succeed:

  <system.net>
    <defaultProxy enabled="true" useDefaultCredentials="true">
      <proxy bypassonlocal="true" proxyaddress="http://address:port" />
    </defaultProxy>
  </system.net>

In .Net Core I have tried several ways of setting the proxy including setting the ProxyAddress in the BasicHttpBinding. When doing this I receive the (407) Proxy Authentication Required response. I believe this is due to not being able to set the useDefaultCredentials="true" portion in the binding.

In full .Net framework if I set useDefaultCredentials="false" I also receive the exact error of (407) Proxy Authentication Required.

Is there a way to set this to use default credentials when using a proxy?

I've been doing something similar, but instead of generating a new binding i'd like to utilize a proxy class generated by Visual Studio 2019.

var b_custom = client.Endpoint.Binding as System.ServiceModel.Channels.CustomBinding;
            
if (b_custom != null)
{
   var htbe = b_custom.Elements.Find<HttpTransportBindingElement>();
   htbe.ProxyAddress =  new Uri(string.Format("http://{0}:{1}", address, port));
   htbe.ProxyAuthenticationScheme = System.Net.AuthenticationSchemes.Anonymous; // Or whatever authentication mechanism your proxy server uses
   htbe.UseDefaultWebProxy = false;
   return;
}

however on windows 10 / core 2.2 that throws the following exception:

InvalidOperationException: When using a non-null Proxy, the WindowsProxyUsePolicy property must be set to WindowsProxyUsePolicy.UseCustomProxy.

That error message comes from WinHttpHandler. WCF stopped using that class directly quite a while ago and we now only reference HttpClientHandler. As of .NET Core 2.1, the default implementation is no longer WinHttpHandler and instead uses the newer SocketsHttpHandler. I suspect you are using a really old release of WCF. Can you make sure you are using the latest versions of System.ServiceModel.*. There was a bug in an earlier version around setting the proxy values on WinHttpHandler and I suspect you are running into that issue.

Thanks. I kind of expected that the required parts are installed and used in the up-to date version either by the .net core 2.2 installation or VS 2019.

After telling the package-manager to lift all System.ServiceModel's from 4.4.4 to 4.5.3 the Exception vanishes and the proxy is used as configured.

According to ConnectedService.json the WCF in charge was 15.0.21025.787

Thanks!

This solved it for me. I was also receiving the exception "When using a non-null Proxy, the WindowsProxyUsePolicy property must be set to WindowsProxyUsePolicy.UseCustomProxy.", which then disappeared once I updated all System.ServiceModel libs. Cheers!

Looks like IntegratedWindowsAuthentication isn't supported. It's a flag that includes Negotiate and Ntlm so I've changed mine to use Ntlm instead - which has worked insomuch as it's moved me on to a different error, sigh.

Thanks for responding!

As you've already worked out, IntegratedWindowsAuthentication has a value of 6, Negotiate has a value of 2 and Ntlm has a value of 4. This means that IntegratedWindowsAuthentication isn't an authentication scheme in it's own right, it's a convenience value to mean Negotiate | Ntlm. We can't accept two different schemes being specified which is why IntegratedWindowsAuthentication isn't supported. The description for Negotiate is:

Negotiates with the client to determine the authentication scheme. If both client and server support Kerberos, it is used; otherwise, NTLM is used.

The only time when this won't work is when integrated Windows authentication isn't enabled on the proxy server but NTLM is. In which case specifying NTLM is needed. Otherwise Negotiate should generally work for you.