As per https://ecosystem.atlassian.net/browse/JSDECO-181:

Refined has two apps on the Atlassian Marketplace, Refined for Jira Cloud and Refined for Confluence cloud, that are runs outside of the Atlassian cloud. They make use of the Atlassian rest APIs to display information frmo Confluence, Jira and JSD. To authenticate users we make use of the Atlassian login that supports to add a url to redirect to after login is done
For JSD customers:
xxxxx.atlassian.net/servicedesk/customer/user/login?absolute=true&destination=xxx
For Atlassian users
https://id.atlassian.com/login?continue=$xxxxxx.atlassian.net/login?dest-url=xxx&application=ondemand

When customers get's invited to a service desk or if someone signs up themselves we don't seem to have an option to redirect the user back to refined after sign up. We would need this functionality to make it possible to keep users on the Refined site after sign up.