<system.serviceModel>
  <bindings>
   <basicHttpsBinding>
     <binding name="MyHttpBinding">
       <security mode="TransportWithMessageCredential">
         <transport clientCredentialType="None"></transport>
         <!--<message clientCredentialType="UserName"/>-->
       </security>
     </binding>
   </basicHttpsBinding>
  </bindings>
  <client>
   <endpoint address="https://webserviceURL/services/MyObject"
    binding="basicHttpsBinding" bindingConfiguration="MyHttpBinding"
    contract="MyObject.MyObjectPortType" name="MyObjectHttpPort" />
  </client>
 </system.serviceModel>

ResponseObject responseObj = new ResponseObject();
System.ServiceModel.Description.ClientCredentials clientCredentials = new System.ServiceModel.Description.ClientCredentials();

MyObjectPortTypeClient myClient = new MyObjectPortTypeClient();
myClient.ClientCredentials.UserName.UserName = "username";
myClient.ClientCredentials.UserName.Password = "password";

responseObj = myClient.myMethod(objectWithFieldsToSend)