Authentication sounds simple — users log in and log out. But for a SaaS product, auth includes: social logins, MFA, organization management, role-based access control, SSO, and API key management. Choosing the wrong tool means rebuilding all of this later.

NextAuth (Now Auth.js)

NextAuth is free, open-source, and integrates directly with Next.js. It supports most social providers and works with any database. The trade-off: it requires significant configuration, doesn't have built-in organization management, and you're responsible for the auth UI.

Best for: simple apps with basic auth requirements and developers who want full control.

Auth0

Auth0 is a mature, enterprise-grade auth platform. It supports almost every auth pattern imaginable: SAML, LDAP, enterprise SSO, custom domains, and complex permission systems. It's the right choice for products selling to large enterprises.

Trade-off: it's complex to configure, expensive at scale ($23/month + per-user pricing), and overkill for most early-stage SaaS products.

Best for: enterprise SaaS with SSO requirements and large security teams.

Clerk

Clerk is the modern SaaS authentication platform. It provides:

  • Pre-built, customizable sign-up and sign-in UI components
  • Organizations (multi-tenancy) out of the box
  • Role-based access control with custom roles
  • MFA, passkeys, and social logins included
  • Generous free tier (10,000 MAU free)

Best for: B2B SaaS products that need multi-tenancy, team management, and a polished auth experience without spending weeks building it.

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My Choice: Clerk

I use Clerk on almost every SaaS I build. The Organizations feature alone saves 2–3 weeks of custom development, and the polished UI components mean users have a great experience from signup. The free tier is generous enough that most early-stage SaaS products pay nothing for auth for their first 6–12 months.

Making the Final Choice

For a new SaaS product built on Next.js in 2025, my default recommendation is Clerk for most use cases. The developer experience is excellent, the UI components save significant development time, and the pricing is competitive for early-stage products. If your users are exclusively enterprise customers who require SAML SSO from day one, Auth0 or WorkOS are better choices. NextAuth remains compelling only if you need zero third-party dependencies and are willing to manage the ongoing maintenance yourself.