Mhash extension and system crypt libraries that support crypto
used on LDAP server. It might need PHP LDAP extension with SSL
support, if LDAP server requires it.
-- mysql backend needs PHP MySQL extension.
+- mysql backend needs PHP MySQL extension and PHP 4.3 or later.
- merak backend needs PHP Curl extension.
- peardb backend needs PHP Pear DB libraries (v.1.6.0 or newer) and
PHP extension that is used to connect to database.