System Design Interview: Login Backend

A login backend, or in a more precise term, an identity system is something we interact with every day on the internet. There are countless resources online that detail every aspect of it, but I can’t find a good one that lays out the end to end mechanics from a system design angle. So I would like to give it a try. Bear in mind that this post focuses on the information model of an identity system, which I believe is the core. I’ll start with a username password system and build up the features along the way as I lay out the technicalities.