CE will support IDP shortly.
It will use oxAuth for management of the authentication, so login.config will be irrelevant as long as it is valid.
For now, since you have already figured out proper login handler you can just add line like
to your /opt/tomcat/conf/oxTrust.properties. It should generate userField="uid, mail" in login.config
Please do ldapdelete ou=oxtrust,ou=configuration (accurate dn can be found in /opt/tomcat/conf/oxTrustLdap.properties) after configuration update and before tomcat restart so that configuration is properly updated.