How to authenticate ASP.NET with GitHub

Program.cs

using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authentication.Cookies;
using System.Security.Claims;

var signin = "/signin";
var signout = "/signout";
var callback = "/signin-github";
var redirectUrl = "/";

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorPages();

// wire up the github auth
builder.Services.AddAuthentication(options =>
                {
                    options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                })
                .AddCookie(options =>
                {
                    options.LoginPath = signin;
                    options.LogoutPath = signout;
                })
                .AddGitHub(options =>
                {
                    options.ClientId = builder.Configuration.GetValue<string>("GitHubClientId");
                    options.ClientSecret = builder.Configuration.GetValue<string>("GitHubClientSecret");
                    options.Scope.Add("read:user");
                    options.Scope.Add("gist");
                    options.CallbackPath = callback;

                    options.Events.OnCreatingTicket += context =>
                    {
                        if (context.AccessToken is not null)
                        {
                            var login = context.User.GetString("login");
                            var gitHubId = context.User.GetString("id");
                            var avatar = context.User.GetString("avatar_url");
                            var name = context.User.GetString("name");

                            context.Identity?.AddClaim(new Claim("access_token", context.AccessToken));
                            context.Identity?.AddClaim(new Claim("avatar_url", avatar));
                            context.Identity?.AddClaim(new Claim("full_name", name));
                            context.Identity?.AddClaim(new Claim("github_id", gitHubId));
                        }

                        return Task.CompletedTask;
                    };
                });

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
}

// map the signin and signout endpoints
app.MapGet(signin, async (HttpContext httpContext)
    => await httpContext.ChallengeAsync("GitHub",new AuthenticationProperties { RedirectUri = redirectUrl })
);

app.MapGet(signout, async (HttpContext httpContext)
    => await httpContext.SignOutAsync(new AuthenticationProperties { RedirectUri = redirectUrl })
);

app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthentication();
app.UseAuthorization();
app.MapRazorPages();
app.Run();