public async Task <User> SignUp(User user, string password)
        {
            if (string.IsNullOrEmpty(password) || user == null)
            {
                return(null);
            }
            else
            {
                bool userExists = await _dataContext.Users.
                                  AnyAsync(account => account.Email == user.Email);

                if (!userExists)
                {
                    user.PasswordSalt = ComputeSalt();
                    user.PasswordHash = ComputeHash(password, user.PasswordSalt);

                    await _dataContext.AddAsync(user);

                    await _dataContext.SaveChangesAsync();

                    return(user);
                }
                else
                {
                    return(null);
                }
            }
        }