Clerk
Clerk is a hosted authentication and user management platform with pre-built sign-in, sign-up, and profile components for React, Next.js, and other frameworks, plus organisations and MFA.
Keycloak
Open-source identity and access management platform with SSO, SAML 2.0, OIDC, and LDAP/AD federation — self-hosted, no per-user pricing.
Auth0
Auth0 is Okta's enterprise identity platform, with hosted Universal Login, social and enterprise SSO, MFA, passwordless, and machine-to-machine authorization for web, mobile, and API apps.
Supabase Auth
Supabase Auth is the open-source authentication service built into Supabase, tied to PostgreSQL Row Level Security so the signed-in user's identity drives database access rules.
Firebase Auth
Google's authentication service with deep integration across Firebase platform and extensive mobile SDK support.
BetterAuth
Open-source TypeScript authentication framework that runs inside your app, covering email and password, social OAuth, passkeys, multi-tenancy, and SSO with no per-user pricing, plus an optional paid dashboard.