Request security token with kerberos authentication in AD FS in WinRT

We are currently developing a 8.1 WINDOWS WinRT app using CRM's sdk (blogs.msdn.com/b/crm/archive/2012/11/02/building-clients-for-windows-phone-and-windows-8-rt.aspx)

To authenticate the user using the CRM's service, we must first create a security token request to our AD FS and obtain a SAML token. When send the request with user and pasword based authentication to get the saml with the following code it works fine:

 WSTrustBinding binding;

 IRequestCredentials credentials;

 credentials = new IssuedTokenCredentials(securityTokenResponse);
 binding = new WSTrustBindingUsernameMixed();

 RequestSecurityToken rst = WSTrustFactory.CreateRST(issuerEndpoint.TrustVersion, keyType);

 WSTrustClient trustClient = WSTrustFactory.CreateWSTrustClient(issuerEndpoint.TrustVersion, binding, issuerEndpoint.IssuerAddress, credentials);

 trustClient.IssueCompleted += new EventHandler<IssueCompletedEventArgs>(IssueCompleted);
 trustClient.IssueAsync(rst, callback);

The problem comes when we try to make a request using kerberos based authentication to get the security token,because I can not create a binding using the KerberosWSTrustBinding class in WinRT, because it's not available. It's only available in the framework 4.5.

Is there any option to create a request security token with kerberos authentication in AD FS in WinRT?

Best regards