Program.cs

using System;

using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration.AzureAppConfiguration;

namespace WebApplication4
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateWebHostBuilder(args).Build().Run();
        }

        public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                   .ConfigureAppConfiguration((hostingContext, config) =>
                   {
                       var settings = config.Build();
                       config.AddAzureAppConfiguration(options =>
                       {
                           options.ConnectionString = settings["ConnectionStrings:AppConfig"];
                           // apply configuration for specific region
                           options.Use("*", Environment.GetEnvironmentVariable("REGION_NAME") ?? "Japan East");
                       });
                   })
                   .UseStartup<Startup>();
    }
}