I need a practical recommendation for authentication infrastructure for a new app with React, mobile later, and simple setup.

For a new app with React now and mobile later, and where you want simple setup, my practical recommendation is:

Best default: Clerk

Why it fits:

• Very quick to integrate with React
• Works well for mobile later too
• Handles the annoying auth plumbing for you:
  • sign up / sign in
  • session management
  • social login
  • MFA
  • email verification
  • user management UI
• Good developer experience
• Easy to start small and expand

When to choose something else

Use Auth0 if:

• You need more enterprise features
• You expect complex auth rules, SSO, or large-org customers
• You’re okay with a bit more setup and cost

Use Firebase Auth if:

• You already plan to use Firebase heavily
• You want a very lightweight, fast start
• You’re fine with some auth limitations and more DIY later

Use Supabase Auth if:

• Your backend is already on Supabase/Postgres
• You want a more open, simple stack
• You’re comfortable managing a bit more yourself

My recommendation by scenario

• Fastest clean setup for React + mobile later: Clerk
• Enterprise/compliance-heavy future: Auth0
• Cheap/simple with Firebase backend: Firebase Auth
• Postgres-first app: Supabase Auth

Architecture suggestion

If you choose Clerk:

• React app uses Clerk for login/session
• Your backend verifies Clerk-issued JWT/session
• Later, mobile app uses the same auth provider and token flow

Practical takeaway

If your priority is “I want auth to just work and not become a project”, pick Clerk.

If you want, I can also give you:

1. a decision matrix for Clerk vs Auth0 vs Firebase vs Supabase, or
2. a recommended setup for React + API backend + future mobile.