How to build a secure but open forum based on Solid?

Since data is saved to users’ POD, there should be a way to aggregrate them again, so that forum can provide the list of posts.

One way is crawl data that belongs to some topic, and forum just provide a list of URI of those posts.

If crawler is banned by ACL by default, how can we achieve that?

If crawler is not banned, then somebody may erase the owner metadata, and claim that this post is origined by them.