Navigation bar in custom page in the customer portal

Hi,

We are currently building an addon for Jira Service Desk, and we need to add a new page to the portal for customers to visit.
We have added this page as a servlet with a velocity file. We would like to add the JSD portal top and buttom bar as decorator, but can’t find the decorator. Is there a decorator for Jira Service Desk customer portal that can be used (like atl.general)?

If not, how should we then get the navigation bar from the customer portal?

Best regards
Christian