Create an implementation of 'IStartupFilter' to validate all 'IValidatable' at startup

ConfigValidationStartupFilter.cs

using System;
using System.Collections.Generic;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;

// reference: https://andrewlock.net/adding-validation-to-strongly-typed-configuration-objects-in-asp-net-core/#creating-a-settings-validation-step-with-an-istartupfilter
namespace MyWeb.Filters
{
    public class ConfigValidationStartupFilter : IStartupFilter
    {
        readonly IEnumerable<IValidatable> _validatableObjects;

        public ConfigValidationStartupFilter(IEnumerable<IValidatable> validatableObjects)
        {
            _validatableObjects = validatableObjects;
        }

        public Action<IApplicationBuilder> Configure(Action<IApplicationBuilder> next)
        {
            foreach (var validatableObject in _validatableObjects)
            {
                validatableObject.Validate();
            }

            //don't alter the configuration
            return next;
        }
    }
}

IValidator.cs

namespace MyWeb.Config
{
    public interface IValidatable
    {
        void Validate();
    }
}