public bool Add(RefreshToken refreshToken)
        {
            var existingRefreshToken = _refreshTokenRepository
                                       .GetSingleByCondition(x => x.ClientId == refreshToken.ClientId &&
                                                             x.UserName == refreshToken.UserName);

            if (existingRefreshToken != null)
            {
                var resultRemove = _refreshTokenRepository.Delete(existingRefreshToken);
                if (resultRemove == null)
                {
                    return(false);
                }
            }
            var entity = _refreshTokenRepository.Add(refreshToken);

            if (entity == null)
            {
                return(false);
            }
            _unitOfWork.Commit();
            return(true);
        }