PEAR::Auth uses a number of so called storage containers to store the login data. The following passages describe all of them. If the containers that come with the package don't fit your needs, it is easy to create custom ones, also.
Array
Storage container using a PHP Array.
DB
Storage container using PEAR DB.
DBLite
A simplified version of the DB container that only provides user authentication. No user management functions are provided.
File
Storage container using PEAR File_Passwd.
IMAP
Storage container for use against IMAP servers.
KADM5
Storage container for use against Kerberos V servers.
LDAP
Storage container for use against LDAP servers.
MDB
Storage container using PEAR MDB.
MDB2
Storage container using PEAR MDB2.
Multiple
Storage container for using multiple Auth_Containers in a fall through manner.
PEAR
Storage container for use against the PEAR website.
POP3
Storage container for use against a POP3 server.
RADIUS
Storage container for use against a RADIUS server.
SAP
Storage container for use against a SAP server.
SMBPasswd
Storage container using PEAR File_SMBPasswd.
SOAP
Storage container for use against a SOAP service using PEAR SOAP as the client.
SOAP5
Storage container for use against a SOAP service using PHP5 SOAP as the client.
vpopmail
Storage container using vpopmail.
Custom
Instructions on creating a custom storage container.