If you want to password protect it, you need to create a sub-account for your customer. You can use DriveHQ Group Account service to create sub-accounts for other people. You have full control over sub-accounts, including Create/edit/delete/disable/change password/logon as, etc. You can allocate storage and download bytes to your sub user.
Once you have created an account, you can share a folder to the sub-account and specify a permission level. Your customer can then logon FTP using the sub-account username / password. He can see your shared folders in his \DriveHQShare\ folder.