steam-openid-connect-provider/src/Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace SteamOpenIdConnectProxy
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers()
                .AddNewtonsoftJson()
                .SetCompatibilityVersion(CompatibilityVersion.Version_3_0);

            services.AddDbContext<AppInMemoryDbContext>(options => 
                options.UseInMemoryDatabase("default"));

            services.AddIdentity<IdentityUser, IdentityRole>()
                .AddEntityFrameworkStores<AppInMemoryDbContext>()
                .AddDefaultTokenProviders();

            services.AddIdentityServer(options =>
                {
                    options.UserInteraction.LoginUrl = "/ExternalLogin";
                })
                .AddAspNetIdentity<IdentityUser>()
                .AddInMemoryClients(IdentityServerConfig.GetClients(Configuration["OpenID:ClientID"], Configuration["OpenID:ClientSecret"], Configuration["OpenID:RedirectUri"], Configuration["OpenID:PostLogoutRedirectUri"]))
                .AddInMemoryPersistedGrants()
                .AddDeveloperSigningCredential(true)
                .AddInMemoryIdentityResources(IdentityServerConfig.GetIdentityResources());

            services.AddAuthentication()
                .AddSteam(options =>
                {
                    options.ApplicationKey = Configuration["Authentication:Steam:ApplicationKey"];
                });
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseRouting();
            app.UseIdentityServer();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }
}