SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://www.progress.com/documentation/sitefinity-cms/create-a-custom-endpoint

MyCustomOperationProvider_Global.asax.cs

using System;
using Telerik.Microsoft.Practices.Unity;
using Telerik.Sitefinity.Abstractions;
using Telerik.Sitefinity.Web.Services.Contracts.Operations;

namespace SitefinityWebApp
{
    public class Global : System.Web.HttpApplication
    {

        protected void Application_Start(object sender, EventArgs e)
        {
            ObjectFactory.RegisteringIoCTypes += (object s, EventArgs args) =>
            {
                ObjectFactory.Container.RegisterType(typeof(IOperationProvider), typeof(MyCustomOperationProvider), typeof(MyCustomOperationProvider).Name);
            };
        }
    }
}