Auth has been the target of a lot of SaaS and marketing. It's a menial simple task nobody wants to spend time on. Even if you don't have a huge team I'd rather

Auth has been the target of a lot of SaaS and marketing. It's a menial simple task nobody wants to spend time on. Even if you don't have a huge team I'd rather handroll over using third parties. The mental effort of thinking about some other 3rd party developers or service is not worth it. I can write an auth system in under 100 lines and be on my way to ship features. Social logins are the only annoying thing as they all use slightly different profile fields. If you have issues with scale, scale vertically until it doesn't work anymore. By that point you'll likely have plenty of money to throw around for a registration team to worry about.