Can you recommend a user authentication SDK for adding sign-in to a new developer-facing app?

Yes — for a developer-facing app, I’d usually recommend one of these, depending on how much control vs. speed you want:

Top picks

1. Clerk

Best for: fastest implementation, polished UX, modern dev tooling
Why it’s good:

• Very easy to integrate
• Great sign-in/sign-up UI components
• Supports email/password, magic links, OAuth, SSO, passkeys
• Good for SaaS and developer tools
• Nice React / Next.js experience

Tradeoff: you’re somewhat opinionated into their UI and auth model.

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2. Auth0

Best for: enterprise needs, lots of flexibility, SSO, compliance
Why it’s good:

• Mature and widely adopted
• Strong enterprise auth features
• Excellent support for OAuth/OIDC/SAML
• Good if you expect B2B customers or complex identity requirements

Tradeoff: can get expensive and a bit heavier to set up.

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3. Supabase Auth

Best for: if you’re already using Supabase/Postgres and want a simple backend stack
Why it’s good:

• Easy if your app already uses Supabase
• Supports common auth methods
• Open-source friendly
• Good value for smaller teams

Tradeoff: less polished/auth-focused than Clerk or Auth0 for developer-facing SaaS UX.

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4. Firebase Authentication

Best for: quick launch, especially if you’re already on Google Cloud/Firebase
Why it’s good:

• Quick to get started
• Reliable and scalable
• Good docs and broad provider support

Tradeoff: better for general apps than for a tailored SaaS authentication experience.

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My practical recommendation

If this is a new developer-facing SaaS app, I’d start with:

• Clerk if you want the best developer experience and quickest path to production
• Auth0 if you know you need enterprise/SSO/compliance sooner
• Supabase Auth if you want a simpler, lower-cost stack and already use Supabase

If you want one answer:

Clerk is probably the best default choice for a new developer-facing app.

If you tell me your stack (Next.js, React, backend language, B2B vs B2C, need SSO/passkeys?), I can recommend a more specific option.