IDataService.cs

using App3.Models;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace App3.Services
{
    public interface IDataService
    {
        Task AddUser(string Username, string Password);
        Task<IEnumerable<User>> GetUser();
        Task RemoveUser(int id);
        Task AddUser(object username, object password);
        Task AddUser(string username, object password);
    }
}