We're in the process of making a private service desk for internal issues, where certain personelle and some external users can submit issues to this service desk via direct email.
We do not want this service desk to be visible when users log in to the support portal unless they've been specifically added to this service desk.
For example.. we allow public signup for our main helpdesk in a project called ISSUES. We also allow public signup for our internal helpdesk called II (for Internal Issues).
If someone is added to the system via ISSUES, they should *not* be allowed to see the Internal Issues support desk.

This is my test login to a user that was automatically added by emailing to our ISSUES customer channel. They should not have access to the Internal Issues service desk.