How to resolve error when using [Authorize] in Index.cshtml in ASP.NET?

Question

I got error when I user [Authorize] in Index.cshtml and I don't know how to fixed it. I just would like to make login page to authen when people access webpage and then go to index page if authen was complete.

Startup.cs

public class Startup
{
    public IConfiguration configRoot
    {
        get;
    }
    public Startup(IConfiguration configuration)
    {
        configRoot = configuration;
    }
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddAuthentication().AddCookie("MyCookieAuth", options =>
        {
            options.Cookie.Name = "MyCookieAuth";
            options.LoginPath = "/Account/Login";
        });
        services.AddRazorPages();
    }
    public void Configure(WebApplication app, IWebHostEnvironment env)
    {
        if (!app.Environment.IsDevelopment())
        {
            app.UseExceptionHandler("/Error");
            // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }
        app.UseHttpsRedirection();
        app.UseStaticFiles();
        app.UseRouting();
        app.UseAuthorization();
        app.MapRazorPages();
        app.Run();
    }
}

Index.cshtml.cs

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;

namespace OT6.Pages
{
    [Authorize]
    public class IndexModel : PageModel
    {
        private readonly ILogger<IndexModel> _logger;

        public IndexModel(ILogger<IndexModel> logger)
        {
            _logger = logger;
        }

        public void OnGet()
        {

        }
    }
}

Error

An unhandled exception occurred while processing the request.
InvalidOperationException: No authenticationScheme was specified, and there was no DefaultChallengeScheme found. The default schemes can be set using either AddAuthentication(string defaultScheme) or AddAuthentication(Action<AuthenticationOptions> configureOptions).
Microsoft.AspNetCore.Authentication.AuthenticationService.ChallengeAsync(HttpContext context, string scheme, AuthenticationProperties properties)

InvalidOperationException: No authenticationScheme was specified, and there was no DefaultChallengeScheme found. The default schemes can be set using either AddAuthentication(string defaultScheme) or AddAuthentication(Action<AuthenticationOptions> configureOptions).
Microsoft.AspNetCore.Authentication.AuthenticationService.ChallengeAsync(HttpContext context, string scheme, AuthenticationProperties properties)
Microsoft.AspNetCore.Authorization.Policy.AuthorizationMiddlewareResultHandler.HandleAsync(RequestDelegate next, HttpContext context, AuthorizationPolicy policy, PolicyAuthorizationResult authorizeResult)
Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

enter image description here

Answer 1

The error clearly says you have not added any Authentication Scheme: You need to add a scheme as below:

builder.Services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
    .AddCookie(options =>
    {
        options.ExpireTimeSpan = TimeSpan.FromMinutes(20);
        options.SlidingExpiration = true;
        options.AccessDeniedPath = "/Forbidden/";
    });

Also in the middleware, you need to add "app.UseAuthentication()" middleware, above "app.UseAuthorzation".

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