How to display a confirmation Pop up in Service Portal

Hi Team,

  We have a catalog item and user will be filling the details in the catalog item form in service portal. While user is submitting the request it should display the message stating "Are you sure to submit the request: requested for" and it should contain ok and cancel button. If user is selecting ok it should submit the request. If user is selecting cancel then it should be in the same page. Kindly help me to achieve this,