Why does keystone use 'sn' instead 'cn' or 'local_id' when integrated with Active Directory ?

Issue

• Keystone lists user's Name as 'sn' value instead of 'cn' value from Active Directory .
• Keystone does not list 'local_id' attribue value in keystone.id_mapping table as Name for users .
• Active Directory user names are listed by Surnames with following keystone configuration :

[ldap]
user_tree_dn=ou=production,ou=people,ou=ORG,DC=example,DC=com
user_objectclass=person
user_id_attribute-cn
user_name_attribute=cn
user_mail_attribute=mail