namespace MyMainService
{

    [System.Web.Services.WebServiceBindingAttribute(Name="MyMainServiceImplPortBinding", Namespace="http://webService.main.myService.com/")]
    public partial class MyMainServiceImplService : System.Web.Services.Protocols.SoapHttpClientProtocol {

        public AuthenticationHeader AuthenticationHeaderValue;

        public MyMainServiceImplService() {
            this.Url = "http://.../MyMainServiceImplService";
        }

        [System.Web.Services.Protocols.SoapRpcMethodAttribute("", RequestNamespace="http://webService.main.myService.com/", ResponseNamespace="http://webService.main.myService.com/", Use=System.Web.Services.Description.SoapBindingUse.Literal)]
        [return: System.Xml.Serialization.XmlElementAttribute("return")]
        public string invokeTransaction(string request) {
            object[] results = this.Invoke("invokeTransaction", new object[] {
                        request});
            return ((string)(results[0]));
        }
    }

    public class AuthenticationHeader : SoapHeader
    {
        public string UserName;
        public string Password;
    }
}

using (MyMainService.BlazeMainServiceImplService client = new MyMainService.MyMainServiceImplService())
                {
                    client.AuthenticationHeaderValue = new MyMainService.AuthenticationHeader();
                    client.AuthenticationHeaderValue.UserName = "username";
                    client.AuthenticationHeaderValue.Password = "pwd";

                     ruleServiceResult = client.invokeTransaction(xmlRequest);
                }