Filters not supported for LDAP authentication

Hi,

Is there any reason filters are not supported for search+bind LDAP
authentication?
There is no option to pass a filter in search+bind mode and
"ldapsearchattribute" parameter is even checked to prevent filter injection.
"ldapurl" parameter is defined as an RFC 4516 LDAP URL except filters
and extensions are not supported despite being parsed.

Thanks.

Bastien