Net Core Identity 2.1 Authentication Not Working Correctly Accessing Protected Endpoints

Question

The problem to be described is where an application is intended to be used to authenticate another application and a Login page does not successfully authenticate then correct credentials are entered.

The endpoints in several applications are protected by [Authorize] to ensure the challenge is executed and a Login page displayed. For testing purposes using brand new Net Core applications with default functionality. One application is started running on localhost and the other application started up and logged in to redirect to the first immediately after successful authentication displaying a Login page for that application. This is fine.

If the login credentials are entered incorrectly then "Invalid login attempt" as might be expected. However, when the correct credentials are applied authentication does not take place at all and the Login page is still displayed without redirection and the typed credentials disappear. This does not seem right. Have also tried adding using Cookie authentication but cannot get the cookies to appear, and JWT but don't know where to send the tokens. How do I get this to work? Ideally I would like the first authentication to pass through so the Login page does not appear on the redirection but this may be much more difficult. The Startup.cs code in all the application is shown below to check whether something obvious missing.

    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)
    {
        // Authentication/Authorisation (Identity) Context
        services.AddDbContext<ApplicationDbContext>(options =>
        {
            options.UseSqlServer(Configuration["WCX_Identity_Connection"],
                                sqlOptions => sqlOptions.MigrationsAssembly(typeof(Startup).GetTypeInfo().
                                Assembly.GetName().Name));
        },
            ServiceLifetime.Scoped
        );

        // Configure default Identity implementation
        services.AddDefaultIdentity<ApplicationUser>()
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultUI()
            .AddDefaultTokenProviders()
            .AddEntityFrameworkStores<ApplicationDbContext>();

        // Register no-op EmailSender used by account confirmation and password reset during development
        // For more information on how to enable account confirmation and password reset please visit https://go.microsoft.com/fwlink/?LinkID=532713
        services.AddSingleton<Microsoft.AspNetCore.Identity.UI.Services.IEmailSender, EmailSender>();

        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?}");
        });
    }

The Home Controller code is shown below for the first application and this works perfectly using the Identity tables set up for the applications. The other applications also point to the same database.

 public class HomeController : Controller
{
    [Authorize]
    public IActionResult Index()
    {
        // The home page is redirected dependent on currently logged in user details stored in the Identity tables.
        if (User.Identity.IsAuthenticated)
        {
            using (var context = new WCX_IdentityContext())
            {
                // Use Identity and EF core to retrieve logged on user details
                var identity = (ClaimsIdentity)User.Identity;

                // The AspNetUsers Identity table contains the basic identity details
                var user = context.AspNetUsers.SingleOrDefault(x => x.UserName == identity.Name);

                // The AspNetApplicationUsers table contains the application ids the logged on user is authorised to use
                var appUserIds = context.AspNetApplicationUsers.Where(x => x.UserId == user.Id).Select(y => y.ApplicationId);

                List<ApplicationLink> applicationLinks = new List<ApplicationLink>();
                foreach (var appUserId in appUserIds)
                {
                    // The AspNetApplications table contains the application name and redirect url 
                    var app = context.AspNetApplications.SingleOrDefault(x => x.Id == appUserId);
                    if (app != null)
                    {
                        applicationLinks.Add(new ApplicationLink
                        {
                            ApplicationName = app.ApplicationName,
                            AppUrl = app.AppUrl
                        });
                    }
                }

                if (applicationLinks.Count == 0)
                {
                    // Redirect to display no applications available
                    return RedirectToAction("Unavailable");
                }
                else if (applicationLinks.Count == 1)
                {
                    // Redirect to application url
                    return Redirect(applicationLinks[0].AppUrl);
                }
                else
                {
                    // Show hyperlinks on home page
                    return View(applicationLinks);
                }
            }
        }

        return View();
    }