This doc goes into more detail -

https://github.com/nyblnet/bento/blob/main/docs/security.md

But basically when your bento HTML first gets saved, it generates a number of keys used for managing the permissions to join the Cloudflare DO. You can then send out an invite deck with a key that allow other people to join (with their own generated keys). With this architecture, you can revoke people's access, as well as giving them only read-access to the sharing session for example.