CustomActionCallPlugin.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.Xrm.Sdk;

namespace Sample_Plugin
{
    public class CustomActionCall : IPlugin
    {
        public void Execute(IServiceProvider serviceProvider)
        {
            IPluginExecutionContext context =
                (IPluginExecutionContext)serviceProvider.GetService(typeof(IPluginExecutionContext));
            IOrganizationServiceFactory factory =
                (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
            IOrganizationService service =
                factory.CreateOrganizationService(context.UserId);

            var MyInputParam = (string)context.InputParameters["MyInputParam"];

            context.OutputParameters["MyOutputParam"] = "This is output parameter";
        }
    }
}