NullReferenceException when using proxy server with NTLM authentication and BasicHttpBinding (... and potentially others)

When using BasicHttpBinding (or potentially others) behind a web proxy that requires authentication, the authenticationScheme cannot be used, as when it comes to opening the http channel, a NullReferenceException is raised in System.Private.ServiceModel.dll when trying to use an uninialized class member.

Root cause: the credential manager only gets instantiated when using authentication against the service itsself but the proxy authentication, which actually can be different (and is in most cases in large enterprise scenarios) is being ignored, even if passed by the used binding.

Code to reproduce:

 private Binding CreateBinding()
 {
           BasicHttpBinding binding = new BasicHttpBinding();
            if (this.ServiceUri.OriginalString.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
            {
                binding.Security.Mode = BasicHttpSecurityMode.Transport;
            }
            else
            {
                binding.Security.Mode = BasicHttpSecurityMode.None;
            }
            binding.CloseTimeout = TimeSpan.FromSeconds(2);
            binding.OpenTimeout = TimeSpan.FromSeconds(5);
            binding.ReceiveTimeout = TimeSpan.FromMinutes(2);
            binding.SendTimeout = TimeSpan.FromMinutes(2);
            binding.MaxBufferSize = Int32.MaxValue;
            binding.MaxReceivedMessageSize = Int32.MaxValue;
            binding.AllowCookies = true;


            CustomBinding customBinding = new CustomBinding(binding);
            if (this.IsProxyEnabled)
            {
                HttpTransportBindingElement httpElement = customBinding.Elements.Find<HttpTransportBindingElement>();
                httpElement.UseDefaultWebProxy = false;
                httpElement.ProxyAddress = new Uri($"http://{this.ServiceSettings.ProxyHostname}:{this.ServiceSettings.ProxyPort}");
                httpElement.ProxyAuthenticationScheme = AuthenticationSchemes.Ntlm; // produces NullReferenceException in WCF client (master) during execution
                //httpElement.AuthenticationScheme = AuthenticationSchemes.Ntlm; // nicht richtig - das hier wäre für die authentifizierung am Webservice selbst
                httpElement.BypassProxyOnLocal = false;
            }
            return customBinding;
}

[dimalyshev]

@mconnew, sorry in advance for mess with this 2 prev PR - I really don’t know how to purge these artifacts from issue history. But #4563 really fixes issue with Proxy with Basic auth and gets relief with all this nightmares about configuring binding proxy.

The exception call stack for #4562 is here:

System.InvalidOperationException: The required UserNameSecurityToken was not provided.
   at System.Runtime.AsyncResult.End[TAsyncResult](IAsyncResult result) in \wcf\System.Private.ServiceModel\src\Internals\System\Runtime\AsyncResult.cs:line 354
   at System.ServiceModel.Channels.ServiceChannel.SendAsyncResult.End(SendAsyncResult result) in \wcf\System.Private.ServiceModel\src\System\ServiceModel\Channels\ServiceChannel.cs:line 1909
   at System.ServiceModel.Channels.ServiceChannel.EndCall(String action, Object[] outs, IAsyncResult result) in \wcf\System.Private.ServiceModel\src\System\ServiceModel\Channels\ServiceChannel.cs:line 806
   at System.ServiceModel.Channels.ServiceChannelProxy.TaskCreator.<>c__DisplayClass1_0.<CreateGenericTask>b__0(IAsyncResult asyncResult) in \wcf\System.Private.ServiceModel\src\System\ServiceModel\Channels\ServiceChannelProxy.cs:line 184
--- End of stack trace from previous location where exception was thrown ---

[dimalyshev]

httpElement.ProxyAuthenticationScheme = AuthenticationSchemes.Basic; // produce UsernameSecurityToken error