Auth0 costs ~$0.023 per active user per month at the volumes most Indian D2C startups operate at. For a brand at 100,000 MAU that's ~$2,300/month. For a 1M MAU app, it's ~$23,000/month. Which is fine if your gross margin per user is $5+. It's not fine if your average customer spends ₹300 a month on milk subscriptions. This is the calculation that drives most of our Xenotix Labs backend decisions. Build the auth system, save the recurring fee. Buy the auth system, save 4 weeks of engineering. The right answer changes by company, and we've made both calls. Here's the framework we use.…