Idea comes from pain point with indexing content from Lens. We selectively index content posted from more reputable clients (Phaver/Orb/Lenster), but no way to verify content was actually published from either of those apps.
Potential flow would be: 1) client generates key pair and publishes pub key 2) app signs message and adds signature before publishing to hub 3) external clients index message if signature came from client in whitelisted client list