After successful authentication by a user, the user's profile is retrieved. This field specifies a second LDAP attribute to search from if a search on the first LDAP attribute fails to locate a matching user profile. Primarily, this attribute will be used when the user identification returned from an authentication module is not the same as that specified in User Naming Attribute. For example, a RADIUS server might return abc1234 but the user name is abc. There is no default value for this attribute.
The field will take any valid LDAP attribute (for example, cn).