API

  bool pam_auth(string $username, string $password
                [, string &$error [, $checkacctmgmt = true [, string $servicename ] ] ])
  bool pam_chpass(string $username, string $oldpassword, string $newpassword
                [, string &$error [, string $servicename ] ])

 The parameters are
 
   username		- Username to check
   password		- User supplied password
   error		- Output parameter to put any error messages in
   checkacctmgmt	- Call pam_acct_mgmt() to check account expiration and access hours (requires root access!)
   servicename		- PAM service name to use (provided pam.force_servicename is not TRUE)
   oldpassword		- Current password on account
   newpassword		- Password to change to

INSTALLATION

  For pam_auth and pam_chpass to work, module must know about the PAM service to use.

  By default, the PAM service is set to "php". It can be changed by adding the following
  to your php.ini:

  pam.servicename = "your-pam-service";

  Service name can also be, optionally, passed as a parameter to pam_auth OR pam_chpass.

  You can inform the module to ignore the service name passed as a parameter and use
  pam.servicename only, by adding the following to your php.ini:

  pam.force_servicename = 1;

  Next, you'll need to create a pam service file for php. If you are on linux,
  you'll need to create the file /etc/pam.d/php. You can copy another one to work
  off of (/etc/pam.d/login is a good choice).

  Some examples that should work:

  on linux:

# /etc/pam.d/php
#
# note: both an auth and account entry are required

auth	sufficient	/lib/security/pam_pwdb.so shadow nodelay
account	sufficient	/lib/security/pam_pwdb.so

  on solaris:

# add to /etc/pam.conf

php	auth	requisite	/usr/lib/security/pam_authtok_get.so.1
php	auth	required	/usr/lib/security/pam_unix_auth.so.1
php	account	required	/usr/lib/security/pam_unix_account.so.1

  These would authenticate out of the unix password and shadow file. However 
  please checking other /etc/pam.d/ entries, as the libraries these examples
  point to may not be correct.
  
  
FAQ

 * What is PAM?
 
 PAM stands for Pluggable Authentication Module. It is a system that abstracts
 user authentication to allow arbitrary modules to handle the real work. In this
 way, pam enabled services can use a variety of complex authentication schemes
 without modifying the applications. For more Information, and available
 modules, see http://www.kernel.org/pub/linux/libs/pam/.
 
 
 * Why would I want to use PAM from PHP?
 
 PAM gives you very flexible control over authentication. As an example, there
 are PAM modules that will authenticate against a local shadow or password file,
 a Windows NT domain, an SQL database, LDAP, Kerberos, Radius, and more. In
 addition, pam modules can give you the ability to have restrictions on the
 authentication, such as the pam_tally module which limits the number of login
 attempts, and the pam_listfile which let's you restrict access to a list of
 users. Please note, using pam does not mean you can securely authenticate
 users, it simply gives you the ability to do so with proper configuration and
 planning.
 
 
 * How can I get pam?
 
 If you are running linux or solaris, you already have it! Linux and Solaris
 both natively use pam for all authentication, so you're are all set. If you are
 on other systems, well, you're on your own. I have no idea what PAM has been
 ported too...
 
 
 * I'm getting an Authentication Failure error, why?
 
 Try setting the $checkacctmgmt parameter to false to skip the pam_acct_mgmt() 
 call, note that this only checks the password and skips performing account 
 validation such as account expiration and access. Otherwise see below.
 
 The most likely reason for this is that you are trying to authenticate via a
 local shadow file and you do not have permission to do so. The PAM modules
 handling shadow authentication (used on Linux and Solaris) require that the
 application have permission to read the shadow file (makes sense, eh?). If you
 are running php as a cgi or as a webserver module, it is executed as your
 webservers user and group. 
 
 By default, most Linux and Solaris systems are configured to only allow the root
 user to read the shadow file. The recommended
 way around this is to change permissions on the shadow file so that it is group
 readable, and chgrp the file to the a group that the webserver is in. Before
 doing this, you should give it some serious thought as allowing your webserver
 to read the shadow file gives hackers another way to crack away at your system.
 
 If you decide to enable this, I stronly suggest usage of the pam_tally module
 to limit failed logins to a reasonable number of attempts, and one of the other
 modules which will allow you to block root and other system users.
 
 
 * The pam_auth function doesn't return anything, whattup?
 
 Did you remember to create an entry in the pam configuration for the php
 service?
 
 
 * Logs indicate pam authenticated the user, but the function doesn't return 
 true, what gives?
 
 Make sure your pam configuration has an entry for both auth and account, if you
 do not have both, it will not work.