Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Migrations;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using vue_blog.Data;

namespace vue_blog
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var Host = CreateHostBuilder(args).Build();
            using (var service = Host.Services.CreateScope())
            {
                var ctx = service.ServiceProvider.GetRequiredService<AppDbContext>();

                if (!ctx.Users.Any())
                {
                    var userManager = service.ServiceProvider.GetRequiredService<UserManager<IdentityUser>>();
                    var adminPassword = Environment.GetEnvironmentVariable("ADMIN_PASSWORD");
                    var admin = new IdentityUser { UserName = "admin" };
                    userManager.CreateAsync(admin, adminPassword).GetAwaiter().GetResult();
                }
            };


            Host.MigrateDatabase().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}