dotnet core custom authorization for demos

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Claims;
using System.Text.Encodings.Web;
using System.Threading.Tasks;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http.Connections;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.SignalR;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

public class Program
{
    public static void Main(string[] args) => WebHost
        .CreateDefaultBuilder(args)
        .UseStartup<Startup>()
        .Build()
        .Run();
}


// https://joonasw.net/view/creating-auth-scheme-in-aspnet-core-2
public class DemoAuthenticationOptions : AuthenticationSchemeOptions
{
    public const string DefaultScheme = "Demo";
}
public class DemoAuthenticationHandler : AuthenticationHandler<DemoAuthenticationOptions>
{
    public DemoAuthenticationHandler(IOptionsMonitor<DemoAuthenticationOptions> options, ILoggerFactory logger, UrlEncoder encoder, ISystemClock clock) : base(options, logger, encoder, clock)
    {
    }

    protected override Task<AuthenticateResult> HandleAuthenticateAsync()
    {
        if (!Request.Query.ContainsKey("user") || string.IsNullOrEmpty(Request.Query["user"]))
        {
            return Task.FromResult(AuthenticateResult.NoResult());
        }

        var claims = new[] { new Claim(ClaimTypes.Name, Request.Query["user"]) };
        var identity = new ClaimsIdentity(claims, Scheme.Name);
        var principal = new ClaimsPrincipal(identity);
        var ticket = new AuthenticationTicket(principal, Scheme.Name);
        return Task.FromResult(AuthenticateResult.Success(ticket));
    }
}
public static class DemoAuthenticationExtensions
{
    public static AuthenticationBuilder AddDemoAuthentication(this AuthenticationBuilder build)
    {
        return build.AddScheme<DemoAuthenticationOptions, DemoAuthenticationHandler>(DemoAuthenticationOptions.DefaultScheme, _ => { });
    }
}


public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddAuthentication(options =>
        {
            options.DefaultAuthenticateScheme = DemoAuthenticationOptions.DefaultScheme;
            options.DefaultChallengeScheme = DemoAuthenticationOptions.DefaultScheme;
        }).AddDemoAuthentication();

        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        app.UseAuthentication();

        app.UseDefaultFiles();
        app.UseStaticFiles();
        app.UseMvc();
    }
}


public class DemoController : ControllerBase
{
    // curl -si http://localhost:5000/whoami?user=mac # 200 OK "mac"
    // curl -si http://localhost:5000/whoami # 204 No Content
    [HttpGet]
    [Route(nameof(WhoAmI))]
    public string WhoAmI() => User.Identity.Name;

    // curl -si http://localhost:5000/secret?user=mac # 200 OK "Secret"
    // curl -si http://localhost:5000/whoami # 401 Unauthorized
    [Authorize]
    [HttpGet]
    [Route(nameof(Secret))]
    public string Secret() => nameof(Secret);
}