This property caches user DNs (distinguished names) locally when derby.authentication.provider is set to LDAP and derby.authentication.ldap.searchFilter is set to derby.user. When you provide a user DN with this property, Derby is able to avoid an LDAP search for that user's DN before authenticating. For those users without DNs defined with this property, Derby performs a search using the default value of derby.authentication.ldap.searchFilter.