.Sh DESCRIPTION
The Pluggable Authentication Modules (PAM) library abstracts a number
of common authentication-related operations and provides a framework
for dynamically loaded modules that implement these operations in
various ways.
.Ss Terminology
In PAM parlance, the application that uses PAM to authenticate a user
is the server, and is identified for configuration purposes by a
service name, which is often (but not necessarily) the program name.
.Pp
The user requesting authentication is called the applicant, while the
user (usually, root) charged with verifying his identity and granting
him the requested credentials is called the arbitrator.
.Pp
The sequence of operations the server goes through to authenticate a
user and perform whatever task he requested is a PAM transaction; the
context within which the server performs the requested task is called
a session.
.Pp
The functionality embodied by PAM is divided into six primitives
grouped into four facilities: authentication, account management,
session management and password management.
.Ss Conversation
The PAM library expects the application to provide a conversation
callback which it can use to communicate with the user.
Some modules may use specialized conversation functions to communicate
with special hardware such as cryptographic dongles or biometric
devices.
See
.Xr pam_conv 3
for details.
.Ss Initialization and Cleanup
The
.Fn pam_start
function initializes the PAM library and returns a handle which must
be provided in all subsequent function calls.
The transaction state is contained entirely within the structure
identified by this handle, so it is possible to conduct multiple
transactions in parallel.
.Pp
The
.Fn pam_end
function releases all resources associated with the specified context,
and can be called at any time to terminate a PAM transaction.
.Ss Storage
The
.Fn pam_set_item
and
.Fn pam_get_item
functions set and retrieve a number of predefined items, including the
service name, the names of the requesting and target users, the
conversation function, and prompts.
.Pp
The
.Fn pam_set_data
and
.Fn pam_get_data
functions manage named chunks of free-form data, generally used by
modules to store state from one invocation to another.
.Ss Authentication
There are two authentication primitives:
.Fn pam_authenticate
and
.Fn pam_setcred .
The former authenticates the user, while the latter manages his
credentials.
.Ss Account Management
The
.Fn pam_acct_mgmt
function enforces policies such as password expiry, account expiry,
time-of-day restrictions, and so forth.
.Ss Session Management
The
.Fn pam_open_session
and
.Fn pam_close_session
functions handle session setup and teardown.
.Ss Password Management
The
.Fn pam_chauthtok
function allows the server to change the user's password, either at
the user's request or because the password has expired.
.Ss Miscellaneous
The
.Fn pam_putenv ,
.Fn pam_getenv
and
.Fn pam_getenvlist
functions manage a private environment list in which modules can set
environment variables they want the server to export during the
session.
.Pp
The
.Fn pam_strerror
function returns a pointer to a string describing the specified PAM
error code.