You should be able to login into keycloak using the mail (mailPrimaryAddress) address from the user.
Added the correct mappers to keycloak user federation. univention-keycloak.yaml f738594f42bb | Bug #55458: update advisory 1259746243e5 | Bug #55458: Modify default mappers in keycloak user federation univention-keycloak (1.0.2) 1259746243e5 | Bug #55458: Modify default mappers in keycloak user federation Package: univention-keycloak Version: 1.0.2A~5.0.0.202211301053 Branch: ucs_5.0-0 Scope: errata5.0-2
Package built: OK Package update successful: OK Users can login with their primaryMailAddress: OK YAML:OK Verified
<https://errata.software-univention.de/#/?erratum=5.0x501>