Find the local user that corresponds to an inbound Slack handle. Used
by receive to resolve a sender. Returns null if no local user has
that handle.
Note: receive authenticates senders via NaCl Box (the sender's pubkey
is an input to asymmetric_decrypt); this lookup just tells us which
user record to use for that key. An attacker who can post as @bob on
Slack but who does not hold bob's NaCl private key cannot produce a
blob that decrypts under bob's pubkey.
Find the local user that corresponds to an inbound Slack handle. Used by
receiveto resolve a sender. Returns null if no local user has that handle.Note:
receiveauthenticates senders via NaCl Box (the sender's pubkey is an input to asymmetric_decrypt); this lookup just tells us which user record to use for that key. An attacker who can post as@bobon Slack but who does not hold bob's NaCl private key cannot produce a blob that decrypts under bob's pubkey.