Nsecs are generated by combining the ActivityPub ID with a secret key and then hashing it. It's technically custodial keys I guess, but they're not stored in a database, just computed at runtime and cached for the duration of the session.
Discussion
Thanks nostr:npub108pv4cg5ag52nq082kd5leu9ffrn2gdg6g4xdwatn73y36uzplmq9uyev6, I guess I understood it correctly! What is the risk of a key becoming compromised?