public async Task <User> Authenticate(string username, string password)
        {
            if (string.IsNullOrEmpty(username) || string.IsNullOrEmpty(password))
            {
                return(null);
            }

            var user = await _context.GetuserByUsername(username);

            if (user == null)
            {
                return(null);
            }

            if (password != user.Password)
            {
                return(null);
            }

            user.Token    = GenerarToken(user);
            user.Password = null;

            return(user);
        }