Sample Episerver initialization module to add convention based Web API routes in an Add-On

ApiHttpRoutesInitializationModule.cs

using System.Web.Http;
using EPiServer.Framework;
using EPiServer.Framework.Initialization;

namespace AlloyFindWithWebApi.Business.Initialization
{
    [InitializableModule]
    [ModuleDependency(typeof(EPiServer.Web.InitializationModule))]
    public class ApiHttpRoutesInitializationModule : IInitializableModule
    {
        public void Initialize(InitializationEngine context)
        {
            // get the HttpConfiguration and then add our "custom" routes to the Routes collection
            var httpConfig = GlobalConfiguration.Configuration;

            httpConfig.Routes.MapHttpRoute(
                "CustomWebApiRouteTemplate",
                routeTemplate: "custom-api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
                );
            // use the httpConfig instance to register other routes as you need
        }

        public void Uninitialize(InitializationEngine context)
        {
        }
    }
}