The apiauth directive specifies what users and/or groups are allowed to connect to a specific API group name. The syntax is simple
apiauth apigroupname [uid=uid1,uid2 ...] [gid=gid1,gid2 ...]
You can specify either a uid list, or a gid list, or both. However you must specify either a uid list or a gid list. If you include both a uid list and a gid list, then a process is authorized to connect to that API group if if it is either in the uid-list or it is in the gid-list.
The API group name default has special meaning. If it is specified, it will be used for authorizing clients without any API group name, and all client groups not identified by any other apiauth directive.