What auth service should I use for a new app?

It depends on your app’s size, tech stack, and how much auth you want to own. Here’s a practical way to choose:

Good default picks

If you want the fastest path for a new app

Clerk or Auth0

• Easy to set up
• Good user management, social login, passwordless, MFA
• Nice hosted UI
• Best if you want to move quickly and don’t want to build auth screens yourself

If you’re already on Firebase / want mobile-first

Firebase Authentication

• Very easy for app + mobile
• Good for social login and phone auth
• Works well with Firestore/FCM
• Less ideal if you want deep enterprise auth features or very customized flows

If you want more control and lower vendor lock-in

Supabase Auth

• Great if you’re already using Supabase/Postgres
• Open-source-ish ecosystem and more backend control
• Solid for email/password, magic links, OAuth
• Good choice for many startups

If you’re building with Next.js and want a developer-friendly OSS option

Auth.js (NextAuth)

• Great for custom implementations
• Open source, flexible
• You manage more of the UX/integration yourself
• Best if you’re comfortable wiring things up

If enterprise SSO / compliance matters

Auth0 or WorkOS

• SSO, SCIM, SAML, enterprise identity workflows
• Better for B2B SaaS
• Usually more expensive, but much easier than building enterprise auth yourself

Quick decision guide

Choose Clerk if:

• You want the best developer experience for a modern web app
• You want polished sign-in/sign-up pages out of the box
• You’re building SaaS and want to ship quickly

Choose Auth0 if:

• You need enterprise features or expect them soon
• You want a mature, widely used platform
• Budget is less of a concern

Choose Firebase Auth if:

• You’re building mobile apps or already use Firebase
• You want simple social login/phone auth
• You prefer managed backend services

Choose Supabase Auth if:

• You want auth tied to Postgres/Supabase
• You want a lower-cost, more flexible setup
• You’re comfortable handling some auth UX yourself

Choose Auth.js if:

• You want open source and maximum control
• You don’t mind building more of the integration yourself

My recommendation for most new apps

• B2C SaaS / web app: Clerk
• B2B SaaS with SSO needs: Auth0 or WorkOS
• Mobile-first or Firebase stack: Firebase Auth
• Postgres/Supabase stack: Supabase Auth
• Next.js + custom control: Auth.js

Important factors to check

Before deciding, consider:

• Social logins needed?
• Passwordless / magic links?
• MFA?
• Enterprise SSO (SAML/OIDC)?
• User management/admin dashboard?
• Email deliverability and templates?
• Pricing at your expected user count?
• Ability to migrate later?

If you want, I can give you a specific recommendation if you tell me:

1. your stack (Next.js, React Native, Flutter, etc.)
2. whether it’s B2B or B2C
3. whether you need SSO/MFA/passwordless
4. expected user scale and budget