This is a major rewrite of pam_krb5afs.  Call it 2.x, for lack of a better term.

o Compared to the earlier releases, this tree builds a single module which
  "knows" how to do everything which is knowable at compile-time.
o Configuration options which can now be set as library defaults in the
  system-wide krb5.conf are now largely ignored by the module.

Standard options:
o debug
  Log debugging messages at LOG_DEBUG priority.
o debug_sensitive
  Even log passwords when logging debugging messages at LOG_DEBUG priority.
o no_warn
  When authenticating, don't warn the user about an expired password.
o use_authtok
  When changing passwords, never prompt for password data.  Instead, use
  data stored by a previously-called module.
o use_first_pass
  When authenticating, never prompt for password data.  Instead, use a
  password which was stored by a previously-called module.
o try_first_pass
  When authenticating, first try to authenticate using the password which
  was stored by a previously-called module.  If it fails, then prompt for
  the correct password and try again.

Recognized options (krb5.conf's appdefaults/pam section, and command-line):
o banner=Kerberos
  When changing passwords, tell users that they are changing their Kerberos
  passwords (unset to avoid using any term other than "password").
o ccache_dir=/tmp
  Directory in which to store ccache and ticket files.
o chpw_prompt
  Allow expired passwords to be changed during authentication attempts.  While
  this is the traditional behavior exhibited by "kinit", it is inconsistent
  with the behavior expected by PAM, which expects authentication to (appear to)
  succeed and to have password expiration be flagged by the account management
  function.  Some applications which don't handle password expiration will fail
  incorrectly if the user's password is correct but expired, and setting this
  flag attempts to work around the bug.
o existing_ticket
  Use the presence of a TGT for the user's realm in the default ccache as
  sufficient proof of the user's identity.  If you're not also validating
  credentials, then THIS IS VERY DANGEROUS.
o external
  external = service1 service2
  Attempt to reuse credentials stored in a ccache pointed to by the KRB5CCNAME
  variable in the PAM environment.  This is mainly useful for situations where
  the calling application authenticated the user using GSSAPI, the user
  delegated credentials to the calling application, and you're using pam_krb5
  to obtain a v4 Kerberos ticket via krb524, or AFS tokens.  The calling
  application MUST ensure that KRB5CCNAME points to a ccache which should be
  used for the authenticating user.
o ignore_afs
  Disable the default behavior of attempting to obtain tokens for the local
  AFS cell on behalf of clients.
o ignore_unknown_principals
  ignore_unknown_spn
  ignore_unknown_upn
  Controls whether or not users with unknown principal names should trigger
  a PAM_IGNORE error instead of a PAM_USER_UNKNOWN error.
o initial_prompt
  Controls whether or not pam_krb5 should ask for the user's password, or let
  libkrb5 do it as needed.
o keytab=/etc/krb5.keytab
  Default keytab to use when validating initial credentials.  Can be overridden
  at configure-time.
o krb4_convert
  Obtain Kerberos IV ticket files, even if not required for the sake of AFS.
o krb4_convert_524
  If pam_krb5 is configured to obtain Kerberos IV tickets (see krb4_convert,
  above), this option controls whether or not pam_krb5 attempts to use the
  krb524 service to obtain them in addition to contacting the KDC.  This
  option is enabled by default if "krb4_convert" is enabled, but can be
  disabled using the "no_krb4_convert_524" flag.
o krb4_use_as_req
  If pam_krb5 is configured to obtain Kerberos IV tickets (see krb4_convert,
  above), this option controls whether or not pam_krb5 attempts to use the
  usual kinit-style network request to obtain them.  This option is enabled by
  default if "krb4_convert" is enabled, but it can be disabled using the
  "no_krb4_use_as_req" flag.
o mappings = regex regex [regex regex...]
  Specifies that pam_krb5 should derive the user's principal name from the Unix
  user name by first checking if the user name matches the first regex, and
  if it matches, formulating a principal name using the second regex.  Multiple
  pairs of regular expressions can be used.
  For example,
    mappings = EXAMPLE\\(.*) $1@EXAMPLE.COM
  would map any user with a name of the form "EXAMPLE\whatever" to a principal
  name of "whatever@EXAMPLE.COM".  This is primarily targeted at allowing
  pam_krb5 to be used to authenticate users whose user information is provided
  by winbindd.
  Note that this will frequently require the reverse to be configured by
  setting up an auth_to_local rule elsewhere in krb5.conf.
o minimum_uid=NUMBER
  Minimum UID which the user must have before pam_krb5.so will attempt to
  authenticate that user, otherwise it will ignore the user.
o multiple_ccaches
  Specifies that pam_krb5 should maintain multiple credential caches for
  the application, which sets credentials and opens a PAM session, but
  sets the KRB5CCNAME variable after doing only one of the two.  This
  option is usually not necessary for most services.
o no_user_check
  Go ahead and authenticate users for whom getpwnam() returns no information.
  Credential cache and ticket files will be created and owned by the current
  user and group ID instead of the user's.
o null_afs
  Attempt to get credentials for AFS by guessing a service name of the form
  afs@REALM first, and then one of the form afs/cell@REALM, rather than
  proceeding in the opposite order.
o realm=REALM
  Override the default realm.
o renew_lifetime
  Override the default renewable lifetime (set in libdefaults, else 0).
o subsequent_prompt
  Controls whether or not pam_krb5 should just return the PAM_AUTHTOK when
  libkrb5 requests that pam_krb5 get information from the user.
o ticket_lifetime
  Override the default ticket lifetime (24 hours with krb5 1.3, else 10 hours).
  The actual lifetime of your tickets will most likely be the lowest of 1) this
  value, 2) the configured maximum lifetime of your ticket-granting principal,
  3) the configured maximum ticket life for your user principal, and 4) the
  maximum allowable lifetime specified in your KDC's configuration.
o tokens
  Create a new AFS PAG and obtain AFS tokens during the authentication phase.
  By default, tokens are obtained for the local cell (and the cell which
  contains the user's home directory, if they're not the same).
o use_shmem
  use_shmem = service1 service2
  Pass credentials from authentication to session management using shared
  memory instead of PAM data items.  This allows authentication and session-
  managment to be performed in different processes, so long as the PAM
  environment is correctly propagated from one to the other.
o validate
  validate = service1 service2
  Validate initial credentials.  By default, credentials are validated if
  the specified keytab file can be read.

Configuration file only:
o afs_cells = cell1 cell2 cell3 cell4=afs/cell4@EXAMPLE.COM

This module lives in a git repository; for more information, point a
browser at http://fedorahosted.org/pam_krb5/.