kumomta/docs/reference/events/get_egress_source.md

kumo.on('get_egress_source', function(source_name))

kumo.on('get_egress_source', function(source_name)
  return kumo.make_egress_source {
    name = source_name,
    -- other fields here
  }
end)

See also kumo.make_egress_source.