Auth0 has 3 open source alternatives
Identity provider and single sign-on authentik is an open source identity provider. Give users one login for all your apps with SAML, OAuth2 and LDAP, …
Passkeys and login for your app Hanko is open source authentication built around passkeys. Add passkeys, passwords, one-time codes, social logins and SSO to your app …
Authentication for your apps Logto is open source authentication and authorisation. Add sign-in with passwords, passkeys, social logins and single sign-on to your apps, …