How do I tell WCF to skip verification of the certificate?

You might be able to achieve this in Silverlight by allowing cross-domain communication between the web server the hosts the Silverlight application and the remote WCF service.

In that case you need to place a clientaccesspolicy.xml file at the root of the domain where the WCF service is hosted:

<?xml version="1.0" encoding="utf-8"?>
<access-policy>
  <cross-domain-access>
    <policy>
      <allow-from http-request-headers="SOAPAction">
        <domain uri="http://*"/>
      </allow-from>
      <grant-to>
        <resource path="/" include-subpaths="true"/>
      </grant-to>
    </policy>
  </cross-domain-access>
</access-policy>

Here's what MSDN states about this approach:

To allow access to an HTTPS service from any Silverlight control hosted over HTTP application, you need to put the <domain uri=”http://” />* element inside your <allow-from> element.

I haven't tried this myself but it could be worth a shot. Also be sure to check out the following resources for more details:

• Making a Service Available Across Domain Boundaries
• Configuring Web Service Usage in Silverlight Clients

---

Disabling X.509 certificate validation in .NET

For .NET applications this sample WCF configuration will disable validation of both whether the certificate is trusted and whether it is still valid on the client:

<system.serviceModel>
    <behaviors>
      <endpointBehaviors>
        <behavior name="DisableServiceCertificateValidation">
            <clientCredentials>
                <serviceCertificate>
                    <authentication certificateValidationMode="None"
                                    revocationMode="NoCheck" />
                </serviceCertificate>
            </clientCredentials>
        </behavior>
      </endpointBehaviors>
    </behaviors>
    <client>
      <endpoint address="http://localhost/MyService"
        behaviorConfiguration="DisableServiceCertificateValidation"
        binding="wsHttpBinding"
        contract="MyNamespace.IMyService"
        name="MyServiceWsHttp" />
    </client>
</system.serviceModel>

An alternative solution is to provide custom logic to validate the X.509 certificate provided by the service. In that case you will have to modifiy the configuration file according to the following:

<system.serviceModel>
    <behaviors>
      <endpointBehaviors>
        <behavior name="DisableServiceCertificateValidation">
            <clientCredentials>
                <serviceCertificate>
                    <authentication certificateValidationMode="Custom"
                                    customCertificateValidatorType="MyCertificateValidator, Client"
                                    revocationMode="NoCheck" />
                </serviceCertificate>
            </clientCredentials>
        </behavior>
      </endpointBehaviors>
    </behaviors>
    <client>
      <endpoint address="http://localhost/MyService"
        behaviorConfiguration="DisableServiceCertificateValidation"
        binding="wsHttpBinding"
        contract="MyNamespace.IMyService"
        name="MyServiceWsHttp" />
    </client>
</system.serviceModel>

Then create a class that derives from X509CertificateValidator to implement your custom validation logic.

public class MyCertificateValidator : X509CertificateValidator
{
    public override void Validate(X509Certificate2 certificate)
    {
        // Add custom validation logic
        // Throw an exception to fail validation
    }
}

As always, you can find a more detailed example up on MSDN.

This does not look like an certificate validation error. It looks like a webservice configuration error. Can you post the config for your endpoint on the server?

WCF services don't support SSL by default, you need to enable transport security by creating a binding configuration and pointing your endpoint to it with the bindingConfiguration attribute.

Here is a sample binding configuration that supports SSL:

<bindings>
  <basicHttpBinding>
    <binding name="SecureTransport">
      <security mode="Transport">
        <transport clientCredentialType="None"/>
      </security>
    </binding>
  </basicHttpBinding>
</bindings>

and your endpoint config would look like this:

<endpoint address=""
   binding="basicHttpBinding"
   bindingConfiguration="SecureTransport"
   contract="MyServices.IWebService" />