Proxy Authorization

Hi All

I try configure slapd.conf to support proxy authorization but I can not
add authzTo attribute to an entry

[root@masterldap ~]# ldapmodify -x -w secret -D "cn=admin,dc=demo,dc=net"
dn: uid=matt,ou=Users,dc=demo,dc=net
changetype: add
authzTo: dn.regex=^uid=[^,]*,ou=Users,dc=demo,dc=net$

adding new entry "uid=matt,ou=Users,dc=demo,dc=net"
ldap_add: Invalid syntax (21)
        additional info: authzTo: value #0 invalid per syntax

[root@masterldap ~]#


I didn't see an authzTo attribute in any openldap schema .How can I fix
an error?