How do you build auth for your SaaS apps? Do you use a library, like NextAuth? A provider, like Supabase Auth? Do you write your own?

Which one would you recommend, what are some of the best options?

I'm building an app using Next.js and Prisma. I'm currently considering Supabase Auth, Auth0, or writing the auth myself. Writing it myself seems like the simplest solution, but people keep telling me that it's a bad idea and creating truly secure auth is really hard. Although I tried implementing auth with Supabase Auth, and I tried writing my own auth with Google OAuth and Magic Links, and my own auth ended up feeling much nicer and simpler.

I'm looking for some advice from more experienced people. What do you use? What would you recommend? What are the pros and cons of various approaches?