Auth & Identity
Sign-in, SSO, user management.
Auth is the hardest thing to rip out later, because whoever you pick ends up holding your user table. The real fork is architectural: a hosted identity provider like Auth0 or Clerk, something you run yourself like Logto or SuperTokens, or a library such as Better Auth that keeps users in your own database. If enterprise SSO is on the roadmap, confirm it exists before you need it.
Editor's pick
Better Auth if you'd rather own the user table outright. Auth lives in your codebase, against your database, with no account to migrate off later.