It's possible to proof group membership without revealing who you are. So you could have just what nostr:npub1ah3aj4mhfew4c7txfdd4paf3wr5syntkeyxenl9fxf9rejte2wpqwcl76e was referring to. You could use nostr keys for that but the group would have to collaborate to generate some setup ... I'm not a cryptographer but I'm sure it's possible.