The PEAR::Auth package provides methods for creating an authentication
system using PHP.

Currently it supports the following storage containers to read/write
the login data:

* All databases supported by the PEAR database layer
* All databases supported by the MDB database layer
* Plaintext files
* LDAP servers
* POP3 servers
* IMAP servers
* vpopmail accounts
* RADIUS
* SAMBA password files
* SOAP.

WWW: http://pear.php.net/package/Auth/