Why is IdentityServer4 Code Breaking My Identity Project?

Question

I have a working ASP.NET Identity project (based on the Core 2.1 scaffolding). I also have a working IdentityServer4 project (based on the QuickStart examples).

When I try to combine the two into an integrated project, my Identity project breaks - the problem is I can no longer log in.

I'm sure it's the way the middleware is configured in the Startup.cs but I'm have no idea what I'm doing wrong!

Here is the working Identity project (Startup.cs):

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.Configure<CookiePolicyOptions>(options =>
        {
            // This lambda determines whether user consent for non-essential cookies is needed for a given request.
            options.CheckConsentNeeded = context => true;
            options.MinimumSameSitePolicy = SameSiteMode.None;
        });

        services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(
                Configuration.GetConnectionString("DefaultConnection")));
        services.AddDefaultIdentity<ApplicationUser>()
            .AddEntityFrameworkStores<ApplicationDbContext>();

        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
            app.UseDatabaseErrorPage();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
            app.UseHsts();
        }

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

        app.UseAuthentication();

        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });
    }
}

And here is the working IdentityServer4 project (Startup.cs):

public class Startup
{
    private IConfiguration Configuration { get; }

    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

        services.AddIdentityServer()
            .AddDeveloperSigningCredential(filename: "tempkey.rsa")
            .AddInMemoryApiResources(Config.GetApiResources())
            .AddInMemoryIdentityResources(Config.GetIdentityResources())
            .AddInMemoryClients(Config.GetClients())
            .AddTestUsers(Config.GetUsers());
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
            //app.UseHsts();
        }

        app.UseStaticFiles();
        app.UseIdentityServer();
        app.UseMvcWithDefaultRoute();
    }
}

And here is the combine Startup.cs that is broken:

   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.Configure<CookiePolicyOptions>(options =>
        {
            // This lambda determines whether user consent for non-essential cookies is needed for a given request.
            options.CheckConsentNeeded = context => true;
            options.MinimumSameSitePolicy = SameSiteMode.None;
        });

        services.AddDbContext<ApplicationDbContext>(options =>
            options.UseSqlServer(
                Configuration.GetConnectionString("DefaultConnection")));

        services.AddDefaultIdentity<ApplicationUser>()
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();

        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

        services.AddIdentityServer()
            .AddDeveloperSigningCredential(filename: "tempkey.rsa")
            .AddInMemoryApiResources(Config.GetApiResources())
            .AddInMemoryIdentityResources(Config.GetIdentityResources())
            .AddInMemoryClients(Config.GetClients())
            .AddAspNetIdentity<ApplicationUser>();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
            app.UseDatabaseErrorPage();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
            app.UseHsts();
        }

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

        //app.UseAuthentication();
        app.UseIdentityServer();

        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });
    }
}

Any clues?

Answer 1

Got it. Stumbled across the answer here: https://github.com/IdentityServer/IdentityServer4/issues/1900

Specifically, adding this code fixed it:

        services.AddAuthentication(options =>
        {
            options.DefaultAuthenticateScheme = IdentityConstants.ApplicationScheme;
            options.DefaultChallengeScheme = IdentityConstants.ApplicationScheme;
        });

`