code/modules/admin/connectioncheck/bancheck_functions.dm

/proc/_fetch_bans	Checks for bans matching ckey, ip, or cid.
/proc/_unique_ckeys_from_bans	Returns a sorted list containing only each unique ckey present in a list of connections provided by `_fetch_connections()`.
/proc/_find_bans_in_connections	Checks a list of connections for bans matching any of the list entries.