Class<?> implementorClass;
if(moduleKey.service.equals("TestService")){
    implementorClass = findCustomApiEndpointClass(moduleKey);
}
else{
    implementorClass = this.findEndpointClass(moduleKey);
}
if (implementorClass == null) {
    throw new BGException("Не найден сервис: " + moduleKey.module + ":" + moduleKey.service);
}

private Class<?> findCustomApiEndpointClass(ModuleKey moduleKey) {
        try {
            return DynamicClassManager.getInstance().loadClass("api.ru.ellco.bgbilling.test.impl.TestServiceImpl");
        } catch (BGException e) {
            log.error(e.getMessage(), e);
            return null;
        }
    }

"user" :{ "user" : "login", "pswd" : "password" },

package api.ru.bitel.bgbilling.impl;

import java.util.ArrayList;
import java.util.List;
import javax.jws.WebService;
import ru.bitel.bgbilling.kernel.container.service.server.AbstractService;

@WebService(targetNamespace="testService")
public class TestCustomServiceImpl extends AbstractService implements TestCustomService
{
   public List<Integer> testMethod()
   {
      List<Integer> list = new ArrayList<Integer>();
      list.add( 1 );
      list.add( 2 );
      list.add( 3 );
      return list;
   }
}

package api.ru.bitel.bgbilling.impl;

import java.util.List;
import javax.jws.WebService;

@WebService
public interface TestCustomService
{
   public List<Integer> testMethod();
}

http://127.0.0.1:8081/bgbilling/executer/json/test1/TestCustomService

{
    "method": "testMethod",
    "user": {
        "user": "user",
        "pswd": "XXXXX"
    },
    "params": {}
}