I expect the token only gets populated with the relevent URL when it is used as part of a CiviMailing.
The automated message you are referring to does not go out via CiviMail, so it is possible that it will not function in that feature.
If you want to offer them a link to unsubscribe from the group they just signed up to, then you can do so by providing a link with a checksum to civicrm/mailing/subscribe where any Groups that you have set to 'public' will show and they should be able to unsub.
To add this, the url needs &cid={contact.contact_id}&{contact.checksum}
ActuallySince it seems that the checksum doesn't work directly with civicrm/mailing/subscribe?reset=1 but you can set youup a profileProfile that includes your public mailing lists, and send them to that. Bit of a pain having to do the extra steps.
Using tokens for Profiles is detailed here: https://wiki.civicrm.org/confluence/display/CRMDOC/Tokens
And using Profiles for Mailing Lists is here: https://wiki.civicrm.org/confluence/display/CRMDOC/Tokenshttps://docs.civicrm.org/user/en/4.7/email/set-up/#allow-people-to-sign-up-for-your-mailing-lists-online