Keycloak

Keycloak is an open source identity and access management platform. It provides single sign-on for web applications and services and supports OAuth, LDAP and two-factor authentication, so accounts, roles and login flows are handled in one place instead of separately in every application.

Keycloak is a self-hosted open source project rather than a European product: it is a project of the American software company Red Hat. Because you run it yourself, you can place it on European servers and keep the user data under your own control, which is what makes it a European alternative in practice. It suits organisations with the capacity to operate their own identity server.