Three things to never build yourself: auth, notifications, payments
Never outsource Auth. Maintain control over user accounts. That's the life blood of your business. If you have to ask everyone to reset their password because your auth provider increases their pricing or goes out of business, the churn will likely kill your company.<p>I would say the same for Stripe, but at least they'll help you migrate off their platform. Auth providers cant help you because the passwords are hashed... You need the same algo or you cant authenticate using the data they have.<p>And the only way off without a mass password reset is a silent migration in the background: migrate the user when they login.. but we all know that will take months and you will never get 100% to login during the migration period.<p>Pick an auth provider and you better believe in their business as much as your own. You will incur damage when you leave.