Created a custom ApiControllers with Synapse.Server.Extensibility

CustomController.cs

using System;
using System.Web.Http;
using Synapse.Services;

/// <summary>
/// Create a new Class Library (dll) project
/// Add a ref to Synapse.Services.Extensibility from: https://www.nuget.org/packages/Synapse.Server.Extensibility
/// </summary>
namespace Synapse.Custom
{
    [RoutePrefix( "custom" )]
    public class CustomController : ApiController
    {
        [HttpGet]
        [Route( "hello" )]
        public string Hello()
        {
            return "Hello from CustomController, World!";
        }

        [HttpGet]
        [Route( "synapse" )]
        public string SynapseHello()
        {
            IExecuteController ec = ExtensibilityUtility.GetExecuteControllerInstance();
            return ec.Hello();
        }
    }
}

Synapse.Server.config.yaml

# Configure the 'Assemblies' node of Synapse.Server.config.yaml

ServiceName: Synapse.Controller
ServiceDisplayName: Synapse Controller
ServerRole: Controller
WebApiPort: 20000
AuthenticationScheme: IntegratedWindowsAuthentication
SignatureKeyFile: 
SignatureKeyContainerName: DefaultContainerName
SignatureCspProviderFlags: NoFlags
Controller:
  NodeUrl: http://localhost:20001/synapse/node
  SignPlan: false
  Assemblies:
  - Synapse.CustomController
  Dal:
    Type: Synapse.Controller.Dal.FileSystem:FileSystemDal
    Config:
      PlanFolderPath: Plans
      HistoryFolderPath: History
      ProcessPlansOnSingleton: false
      ProcessActionsOnSingleton: true
      Security:
        FilePath: Security
        IsRequired: true
        GlobalExternalGroupsCsv: Everyone
    LdapRoot:
Node:
  MaxServerThreads: 0
  AuditLogRootPath: .\Logs
  Log4NetConversionPattern: '%d{ISO8601}|%-5p|(%t)|%m%n'
  SerializeResultPlan: true
  ValidatePlanSignature: false
  ControllerUrl: http://localhost:20000/synapse/execute