public User Login(LoginInputModel inputModel) { if (inputModel == null || inputModel.Username == null || inputModel.Password == null) { throw new UnauthorizedAccessException("Username or Password is non-existing"); } User foundUser = GetAllUsers().FirstOrDefault(u => u.Username.Equals(inputModel.Username)); if (foundUser == null) { throw new UnauthorizedAccessException("No user registered with such a name"); } AuthenticationHelper.ValidateLogin(foundUser, inputModel); return(foundUser); }