<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.serviceModel>
    <bindings>
      <basicHttpBinding>
        <binding name="BizTalkInterfaceServiceSoapBinding">
          <security mode="Transport">
            <transport clientCredentialType="Basic" proxyCredentialType="Basic" realm="" />
          </security>
        </binding>
      </basicHttpBinding>
    </bindings>
    <client>
      <endpoint address="https://xxx.xxx.xxx.xxx:xxxxx/and/so/on"
          binding="basicHttpBinding" bindingConfiguration="BizTalkInterfaceServiceSoapBinding"
          contract="ServiceReference.BizTalkInterface" name="BizTalkInterfacePort" />
    </client>
  </system.serviceModel>
</configuration>

protected BizTalkInterfaceClient client;

protected ServiceBase()
{
    client = new BizTalkInterfaceClient("BizTalkInterfacePort");
    client.ClientCredentials.Windows.AllowedImpersonationLevel = System.Security.Principal.TokenImpersonationLevel.Impersonation;
    client.ClientCredentials.UserName.UserName = "xxx@xxxdomain";
    client.ClientCredentials.UserName.Password = "xxxxxx";
}