We're using the wpForo plugin as a Service Portal.
We've set it up that all forums, categories and topics can only be seen when logged in.
See the attached image. How can we add a message here when a user comes to the front page - text would tell him that this is a private portal and that he can log in or register using links in menu.
Please check out wpForo "Admin note/message on Forum frontend" feature (Dashboard > Forums > Tools > Misc admin page).
The Admin message will be displayed under the forum breadcrumb menu, above forum and topic titles. you can display the text for certain usergroups.