Step to reproduce

1. Create a page in your Confluence and set the space/page accessible to public/anonymous.
2. Create a Service Desk customer
3. Login to your Service Desk customer portal as the customer you've just created.
4. Access the public page in your Confluence.

Expected Behaviour.

Customer will be able to view the page.

Actual Behaviour.

Confluence throws out User not permitted error

Workaround

Link service desk to that space and enable unlicensed access from the Service Desk UI