User access to login page after authentication

I use identity for authentication in my application, but after authentication the user can access login and register page again!

Login method:

var claims = new List<Claim>()
            {
                new Claim(ClaimTypes.NameIdentifier, user.Id.ToString()),
                new Claim(ClaimTypes.Name, user.Fullname),
            };
            var identity = new ClaimsIdentity(claims, CookieAuthenticationDefaults.AuthenticationScheme);
            var principal = new ClaimsPrincipal(identity);

            var properties = new AuthenticationProperties
            {
                IsPersistent = model.RememberMe
            };
            HttpContext.SignInAsync(principal, properties);

            ViewBag.IsSuccess = true;
            if (ReturnUrl != "/")
            {
                return Redirect(ReturnUrl);
            }

            return Redirect("/dashboard");

startup code:

services.AddAuthentication(options =>
            {
                options.DefaultAuthenticateScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                options.DefaultChallengeScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                options.DefaultSignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;

            }).AddCookie(options =>
            {
                options.LoginPath = "/login";
                options.LogoutPath = "/logout";
                options.ExpireTimeSpan = TimeSpan.FromMinutes(10080);

            });

note: I added app.UseAuthentication() to configure method