[AllowAnonymous]
public class LoginModel : PageModel
{
    private readonly SignInManager<IdentityUser> _signInManager;
    private readonly ILogger<LoginModel> _logger;

    public LoginModel(SignInManager<IdentityUser> signInManager, ILogger<LoginModel> logger)
    {
        .....
    }

    [BindProperty]
    public InputModel Input { get; set; }

    public IList<AuthenticationScheme> ExternalLogins { get; set; }

    public string ReturnUrl { get; set; }

    [TempData]
    public string ErrorMessage { get; set; }

    public class InputModel
    {
        [Required]
        [EmailAddress]
        public string Email { get; set; }

        [Required]
        [DataType(DataType.Password)]
        public string Password { get; set; }

        [Display(Name = "Remember me?")]
        public bool RememberMe { get; set; }
    }

    public async Task OnGetAsync(string returnUrl = null)
    {
            .....
    }

    public async Task<IActionResult> OnPostAsync(string returnUrl = null)
    {
              .....
    }
}