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      know of a case, please let me know.

      By default, `pam_authenticate` intentionally does not follow the PAM
      standard for handling expired accounts and instead returns failure from
      `pam_authenticate` unless the Kerberos libraries are able to change the
      account password during authentication.  Too many applications either do
      not call `pam_acct_mgmt` or ignore its exit status.  The fully correct
      PAM behavior (returning success from `pam_authenticate` and
      `PAM_NEW_AUTHTOK_REQD` from `pam_acct_mgmt`) can be enabled with the
      `defer_pwchange` option.

      The `defer_pwchange` option is unfortunately somewhat tricky to
      implement.  In this case, the calling sequence is:

      ```
          pam_authenticate
          pam_acct_mgmt
          pam_chauthtok
          pam_setcred
          pam_open_session
      ```

      During the first `pam_authenticate`, we can't obtain credentials and
      therefore a ticket cache since the password is expired.  But
      `pam_authenticate` isn't called again after `pam_chauthtok`, so
      `pam_chauthtok` has to create a ticket cache.  We however don't want it
      to do this for the normal password change (`passwd`) case.

      What we do is set a flag in our PAM data structure saying that we're
      processing an expired password, and `pam_chauthtok`, if it sees that
      flag, redoes the authentication with password prompting disabled after
      it finishes changing the password.

      Unfortunately, when handling password changes this way, `pam_chauthtok`
      will always have to prompt the user for their current password again
      even though they just typed it.  This is because the saved
      authentication tokens are cleared after `pam_authenticate` returns, for
      security reasons.  We could hack around this by saving the password in
      our PAM data structure, but this would let the application gain access
      to it (exactly what the clearing is intended to prevent) and breaks a
      PAM library guarantee.  We could also work around this by having
      `pam_authenticate` get the `kadmin/changepw` authenticator in the
      expired password case and store it for `pam_chauthtok`, but it doesn't
      seem worth the hassle.
  - title: History and Acknowledgements
    body: |
      Originally written by Frank Cusack <fcusack@fcusack.com>, with the
      following acknowledgement:

      > Thanks to Naomaru Itoi <itoi@eecs.umich.edu>, Curtis King
      > <curtis.king@cul.ca>, and Derrick Brashear <shadow@dementia.org>, all
      > of whom have written and made available Kerberos 4/5 modules.
      > Although no code in this module is directly from these author's
      > modules, (except the get_user_info() routine in support.c; derived
      > from whichever of these authors originally wrote the first module the
      > other 2 copied from), it was extremely helpful to look over their code
      > which aided in my design.

      The module was then patched for the FreeBSD ports collection with
      additional modifications by unknown maintainers and then was modified by
      Joel Kociolek <joko@logidee.com> to be usable with Debian GNU/Linux.

      It was packaged by Sam Hartman as the Kerberos v5 PAM module for Debian
      and improved and modified by him and later by Russ Allbery to fix bugs
      and add additional features.  It was then adopted by Andres Salomon, who
      added support for refreshing credentials.

      The current distribution is maintained by Russ Allbery, who also added
      support for reading configuration from `krb5.conf`, added many features
      for compatibility with the Sourceforge module, commented and
      standardized the formatting of the code, and overhauled the
      documentation.

      Thanks to Douglas E. Engert for the initial implementation of PKINIT
      support.  I have since modified and reworked it extensively, so any bugs
      or compilation problems are my fault.

      Thanks to Markus Moeller for lots of debugging and multiple patches and
      suggestions for improved portability.

      Thanks to Booker Bense for the implementation of the `alt_auth_map`
      option.

      Thanks to Sam Hartman for the FAST support implementation.