Basically you can set page permissions in Confluence. This way you grant access to pages and their sub-pages to either Internals or Customers. Also see here for official documentation.
Alternatively you can restrict KB articles via labels to certain request types, e.g. if an article is labelled as "internal" and for the request type does only allow the label "customer".
Either way the first solution would be more appropriate here.
By the way: this is the Atlassian community, not the (official) Atlassian support. ;-)
