However, if the Client can provide us with a unique identifier (UUID) indicating a unique user, we don't need to store cookies at all.
The cookie used by Crobox for the Assignment contains a randomly unique identifier (UUID) that tracks the user over multiple sessions. Its expiration date is set to 180 days.
If the Client can send us a UUID, there is no cookie setting required resulting in no Crobox cookie stored at all.
No, the expiration date can be set by the Client according to any desired setting.
Yes. Any user can easily opt-out; Clients don't need any custom integration for this. After opting out, the Crobox tracking cookie (if available) will be deleted and a new cookie will be set indicating that a specific user doesn't want to be tracked over (new) sessions. After opting out, no Data will be collected any more and no profile will be created / updated.