Unable to import RequestFeedbackDetailsService;

Hello

Our client would like to have a possibility to add feedback to resolved SD requests outside of current “Satisfaction” emails. We determined that feedback process is using an unique token(automatically generated) for each issue. In order to get that token we would need to use RequestFeedbackDetailsService, which takes in User and Issue and returns the token. We then could use this token to generate same feedback URL as in the e-mail: /servicedesk/customer/portal/{serviceDeskId}/{issueKey}/feedback?token=…&rating=…
Our first thought was to use Scriptrunner to create REST endpoint that uses RequestFeedbackDetailsService and returns the token, but we got an error importing.
We then tried creating a simple plugin to return this information, but the import still does not work.
Compilation error is “package com.atlassian.servicedesk.api.feedback does not exist”
We have tried adding different versions of “com.atlassian.servicedesk” dependencies with no success:
Is RequestFeedbackDetailsService Interface even accessible? If yes, how do we initialize it?

Thanks in advance,
Raimo