This unique token is a hash that is needed within the link to identify the constituent trying to unsubscribe, so the generic unsubscribe link cannot just be pasted onto an external page, it must be generated. You can generate a valid unsubscribe link using an S38 tag. Here is the syntax:

 [[S38:msg_id]]

where msg_id is the ID of an email message. Traditionally this will be the ID of the email message containing the unsubscribe link, but any valid message ID should work.