European alternatives to Auth0

Auth0 is the customer identity platform Okta acquired in 2021 and continues to sell as a separate product. It covers hosted Universal Login, OIDC, OAuth 2.0, and SAML in both identity-provider and service-provider roles, 40-plus social connections, passwordless and passkey sign-in, and multi-factor authentication.

Developers extend it with Actions, serverless hooks that run inline during login and signup, and use Organizations for B2B multi-tenancy and Fine-Grained Authorization for relationship-based permissions. A free tier runs to 25,000 monthly active users, which is why it is the default choice for startups and side projects.