That's so called "One Click Approval" function many users were dying for.
However, if you want users to login to approve, you can change that token in the email notification template.
Follow the steps below:
1. Add a Content Approval module to a new page. (This module will show all contents pending approval for the current user)
2. Then have the link to this page included in the email template. (So user will click on the link to visit the new page to approve the content).
3. You can set the appropriate permission for that new page. To prevent unauthorized access.
Hope that works for you. :)