public async Task <User> ModifyEmail(string userId, string newEmail)
        {
            var user = await userManager.FindByIdAsync(userId);

            if (user == null)
            {
                throw new DbModelNullException(ExceptionMessageConstants.NullObject);
            }
            if (UserRepositoryExtension.ValidateEmail(newEmail))
            {
                user.Email = newEmail;
                await db.SaveChangesAsync();

                return(user);
            }
            throw new DbModelParamFormatException("Nem megfelelő formátumú email.");
        }
        public async Task <User> ModifyPassword(string userId, string newPassword)
        {
            var user = await userManager.FindByIdAsync(userId);

            if (user == null)
            {
                throw new DbModelNullException(ExceptionMessageConstants.NullObject);
            }
            bool valid = await UserRepositoryExtension.ValidatePassword(newPassword, userManager, user);

            if (valid)
            {
                await userManager.AddPasswordAsync(user, newPassword);

                await db.SaveChangesAsync();

                return(user);
            }
            throw new DbModelParamFormatException("Nem megfelelő a jelszó.");
        }