I’m building a startup and want to move off custom auth. What platform should I use?

If you want to move off custom auth, the best platform depends on how much you want to own vs how fast you want to ship.

My short recommendation

For most startups:

• Best default: Clerk if you want the fastest developer experience and a modern product feel.
• Best enterprise / most flexible: Auth0 if you need lots of control, SSO, and enterprise features.
• Best if you want open-source / self-hostable: Keycloak or FusionAuth.
• Best if you’re already deep in cloud infra: AWS Cognito if cost matters and you can tolerate rough edges.

How to choose

Pick Clerk if:

• You want to replace auth quickly
• You care about a polished sign-in/sign-up UX
• You want built-in user management, orgs, roles, MFA, etc.
• Your team is small and you want less auth plumbing

Tradeoff: less control than rolling your own or using a more infra-heavy solution.

Pick Auth0 if:

• You need enterprise SSO, SCIM, fine-grained rules, or complex identity flows
• You expect larger customers to demand compliance and integrations
• You’re okay paying more for maturity and flexibility

Tradeoff: can get expensive as you scale.

Pick Cognito if:

• You’re cost-sensitive
• You’re already using AWS heavily
• You can accept a less friendly developer experience

Tradeoff: often more integration pain and less polished UX.

Pick Keycloak if:

• You want self-hosted control
• You have infra/DevOps maturity
• You need open-source extensibility

Tradeoff: you own ops, upgrades, and security upkeep.

Pick FusionAuth if:

• You want a self-hostable commercial option
• You want more control than Auth0 with less DIY than Keycloak
• You need flexibility for customer-specific auth setups

Tradeoff: smaller ecosystem than Auth0.

If you’re a typical early-stage startup

I’d usually recommend:

1. Clerk if your app is customer-facing SaaS and speed matters most
2. Auth0 if you expect enterprise sales soon
3. Cognito only if AWS cost/control is a priority
4. Keycloak/FusionAuth if self-hosting is a requirement

Important migration note

Moving off custom auth is not just a sign-in swap. You’ll need to plan for:

• user migration / password migration strategy
• sessions and token handling
• email verification and password reset flows
• roles/permissions mapping
• social login / SSO if needed

If you want, I can give you a recommendation based on your stack (frontend, backend, cloud, B2B/B2C, compliance needs) and narrow it to one platform.