Ask HN: What's a build vs. buy decision that you got wrong?
Not a decision I've got wrong, but I'd suggest authentication services are a common regret. Yes authentication is important to get right, but it's not _that_ complex. SaaS tools for auth are incredibly expensive for the feature set they offer, and are difficult to replace once embedded in your services. SSO in large scale business is a case where buy is the right option but I'd anticipate that for many simpler use cases teams have to work hard to unentangle themselves from Okta etc.