Program.cs

using ContactPro.Data;
using ContactPro.Models;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using ContactPro.Services;
using ContactPro.Services.Interfaces;
using Microsoft.AspNetCore.Identity.UI.Services;
using ContactPro.Helpers;

var builder = WebApplication.CreateBuilder(args);
// var connectionString = builder.Configuration.GetConnectionString("ApplicationDbContextConnection") ?? throw new InvalidOperationException("Connection string 'ApplicationDbContextConnection' not found.");

// Add services to the container.
//var connectionString = builder.Configuration.GetConnectionString("DefaultConnection");
//var connectionString = builder.Configuration.GetSection("pgSettings")["pgConnection"]; //local environment
// The above is what connects to our database. GetSection allows for the 'Secrets' file to be found and selected.
var connectionString = ConnectionHelper.GetConnectionString(builder.Configuration);

// options.UseSqlServer(connectionString)); -- Original
// this version uses PostgreSql
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseNpgsql(connectionString));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();

builder.Services.AddDefaultIdentity<AppUser>(options => options.SignIn.RequireConfirmedAccount = true) //we've extended it. It is no longer IdentityUser but instead AppUser.
    .AddEntityFrameworkStores<ApplicationDbContext>();
builder.Services.AddControllersWithViews();

// Custom Services Start
builder.Services.AddScoped<IImageService, ImageService>(); //this ensures that each user gets their own class so that files aren't somehow mixed up.
builder.Services.AddScoped<IAddressBookService, AddressBookService>();
builder.Services.AddScoped<IEmailSender, EmailService>();

builder.Services.Configure<MailSettings>(builder.Configuration.GetSection("MailSettings")); //this is local use only
// Custom Services End

var app = builder.Build();
var scope = app.Services.CreateScope();
await DataHelper.ManageDataAsync(scope.ServiceProvider); //keep the database updated with the latest migrations.

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseMigrationsEndPoint();
}
else
{
    app.UseExceptionHandler("/Home/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseStatusCodePagesWithReExecute("/Home/HandleError/{0}"); //places listener into application that will redirect to specified errors page.

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthentication();
app.UseAuthorization();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");
app.MapRazorPages();

app.Run();