Register authentication middleware in Startup.cs

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddIdentityCore<AppUser>(options => {
        options.User.AllowedUserNameCharacters = "hojn._";
    });

    services.AddScoped<IUserStore<AppUser>, AppUserStore>();
    
    // Below line registers the authentication service in our app
    // along with a cookie-based authentication scheme named "Cookies"
    // "Cookies" is also set as the default authentication scheme
    services.AddAuthentication(defaultScheme: "Cookies")
            .AddCookie("Cookies");
            
    services.AddControllers();
}