The UNIX authentication service module for PAM provides
  functionality for two PAM categories: authentication and account management.
  In terms of the module-type parameter, they are the
  “auth” and
  “account” features. It also provides a
  null function for session management.
UNIX Ss Authentication Module
The UNIX authentication component provides functions to
  verify the identity of a user (pam_sm_authenticate()),
  which obtains the relevant
  passwd(5) entry. It prompts the
  user for a password and verifies that this is correct with
  crypt(3).
The following options may be passed to the authentication
  module:
  - debug
- syslog(3) debugging
      information at LOG_DEBUGlevel.
- use_first_pass
- If the authentication module is not the first in the stack, and a previous
      module obtained the user's password, that password is used to authenticate
      the user. If this fails, the authentication module returns failure without
      prompting the user for a password. This option has no effect if the
      authentication module is the first in the stack, or if no previous modules
      obtained the user's password.
- try_first_pass
- This option is similar to the use_first_passoption, except that if the previously obtained password fails, the user is
      prompted for another password.
- auth_as_self
- This option will require the user to authenticate himself as the user
      given by getlogin(2), not
      as the account they are attempting to access. This is primarily for
      services like su(1), where the
      user's ability to retype their own password might be deemed
    sufficient.
- nullok
- If the password database has no password for the entity being
      authenticated, then this option will forgo password prompting, and
      silently allow authentication to succeed.
UNIX Ss Account Management Module
The UNIX account management component provides a
  function to perform account management,
  pam_sm_acct_mgmt(). The function verifies that the
  authenticated user is allowed to login to the local user account by checking
  the password expiry date.
The following options may be passed to the management module:
  - debug
- syslog(3) debugging
      information at LOG_DEBUGlevel.
UNIX Ss Password Management Module
The UNIX password management component provides a
  function to perform account management,
  pam_sm_chauthtok(). The function changes the user's
  password.
The following options may be passed to the password module:
  - debug
- syslog(3) debugging
      information at LOG_DEBUGlevel.
- no_warn
- suppress warning messages to the user. These messages include reasons why
      the user's authentication attempt was declined.
- passwd_db=name
- Change the user's password only the specified password database. Valid
      password database names are:
    
      - files
- local password file
- nis
- NIS password database