I may have jinxed it; the other day i was thinking how impressive it is that Microsoft handles their decades old AD/azure/live/xbox/etc auth systems and that th

I may have jinxed it; the other day i was thinking how impressive it is that Microsoft handles their decades old AD/azure/live/xbox/etc auth systems and that they all work together well. In this case, is there another company with a similarly old and complex auth system that does exemplary work?