public async Task <bool> Remove(string username)
        {
            var user = await CosmosDBRepository <User> .GetSingleItemAsync(x => x.Username == username);

            if (user != null)
            {
                await CosmosDBRepository <User> .DeleteItemAsync(user.Id.ToString());

                return(true);
            }

            return(false);
        }
        public async Task <bool> UserExists(string username)
        {
            //if (await _context.Users.AnyAsync(x => x.Username == username))
            //    return true;

            var user = await CosmosDBRepository <User> .GetSingleItemAsync(x => x.Username == username);

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

            return(false);
        }
        public async Task <User> Login(string username, string password)
        {
            //var user =  await _context.Users.FirstOrDefaultAsync(x => x.Username == username);
            var user = await CosmosDBRepository <User> .GetSingleItemAsync(x => x.Username == username);

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

            if (!VerifyPasswordHash(password, user.PasswordHash, user.PasswordSalt))
            {
                return(null);
            }

            return(user);
        }
        public async Task <Book> Details(string id)
        {
            var result = await CosmosDBRepository <Book> .GetSingleItemAsync(id, CollectionId);

            return(result);
        }