in funcframework/events.go [400:406]
func shouldConvertCloudEventToBackgroundRequest(r *http.Request) bool {
_, ok := typeCloudToBackgroundEvent[r.Header.Get("ce-type")]
return ok &&
r.Header.Get("ce-source") != "" &&
r.Header.Get("ce-specversion") != "" &&
r.Header.Get("ce-id") != ""
}