It's so cheap to use a SaaS auth provider like Auth0 or Clerk.dev that you might as well implement one of them. It should take less than a day.
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Of course, many established companies offer SSO, ability to login using Google, Apple, other oauth.
I asked around to my test users and a few potential users and they mentioned email is fine. In my own experience as a SWE I used many softwares at work which used just email login. However, many more offered a bunch more.
Will it be fine to open it up to broader audience without all these things?
I guess if people ask for oauth, I can set it up later and just spend another day and test that everything works. And if they want SSO I'm not sure how that works so I'll have to research it anyway.