If a user (e.g. a JIRA user) is not licensed to use Confluence, they cannot view any Confluence content (from JIRA or Service Desk for instance) - even if that content is available to anonymous users. They currently have to log out before they can see the content. Customers have also asked for anonymous, read-only access for authenticated users that are not coming from a JIRA User Directory.
We cannot allow authenticated but unlicensed users to edit anonymously accessible content, since that would mean that admins would only have to enable anonymous access to have the equivalent of an unlimited user license.
Instead, we should allow authenticated but unlicensed users to get read-only access to confluence content with anonymous permissions.
Such users will still be locked out from parts of the application that require a licensed user, including viewing user profiles, people directories, etc, unless anonymous has been granted permission to view user profiles.
Link JIRA Service Desk project to Confluence space to allow customers to have access to knowledge base in Project Settings -> Knowledge Base.