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pam-krb5 comes with a comprehensive test suite, but it requires some
configuration in order to test anything other than low-level utility
functions.  For the full test suite, you will need to have a running KDC
in which you can create two test accounts, one with admin access to the
other.  Using a test KDC environment, if you have one, is recommended.

Follow the instructions in `tests/config/README` to configure the test
suite.

Now, you can run the test suite with:

```
    make check
```

If a test fails, you can run a single test with verbose output via:

```
    tests/runtests -o <name-of-test>
```

Do this instead of running the test program directly since it will ensure
that necessary environment variables are set up.

The default libkadm5clnt library on the system must match the
implementation of your KDC for the module/expired test to work, since the
two kadmin protocols are not compatible.  If you use the MIT library
against a Heimdal server, the test will be skipped; if you use the Heimdal
library against an MIT server, the test suite may hang.

Several `module/expired` tests are expected to fail with Heimdal 1.5 due
to a bug in Heimdal with reauthenticating immediately after a
library-mediated password change of an expired password.  This is fixed in
later releases of Heimdal.

To run the full test suite, Perl 5.10 or later is required.  The following
additional Perl modules will be used if present:

* Test::Pod
* Test::Spelling

All are available on CPAN.  Those tests will be skipped if the modules are
not available.

To enable tests that don't detect functionality problems but are used to
sanity-check the release, set the environment variable `RELEASE_TESTING`
to a true value.  To enable tests that may be sensitive to the local
environment or that produce a lot of false positives without uncovering
many problems, set the environment variable `AUTHOR_TESTING` to a true
value.

## Configuring

Just installing the module does not enable it or change anything about
your system authentication configuration.  To use the module for all
system authentication on Debian systems, put something like:

```
    auth  sufficient   pam_krb5.so minimum_uid=1000
    auth  required     pam_unix.so try_first_pass nullok_secure
```

in `/etc/pam.d/common-auth`, something like:

```
    session  optional  pam_krb5.so minimum_uid=1000
    session  required  pam_unix.so
```

in `/etc/pam.d/common-session`, and something like:

```
    account  required  pam_krb5.so minimum_uid=1000
    account  required  pam_unix.so
```

in `/etc/pam.d/common-account`.  The `minimum_uid` setting tells the PAM
module to pass on any users with a UID lower than 1000, thereby bypassing
Kerberos authentication for the root account and any system accounts.  You
normally want to do this since otherwise, if the network is down, the
Kerberos authentication can time out and make it difficult to log in as
root and fix matters.  This also avoids problems with Kerberos principals
that happen to match system accounts accidentally getting access to those
accounts.

Be sure to include the module in the session group as well as the auth
group.  Without the session entry, the user's ticket cache will not be
created properly for ssh logins (among possibly others).

If your users should normally all use Kerberos passwords exclusively,
putting something like:

```
    password sufficient pam_krb5.so minimum_uid=1000
    password required   pam_unix.so try_first_pass obscure md5
```

in `/etc/pam.d/common-password` will change users' passwords in Kerberos
by default and then only fall back on Unix if that doesn't work.  (You can
make this tighter by using the more complex new-style PAM configuration.)
If you instead want to synchronize local and Kerberos passwords and change
them both at the same time, you can do something like:

```
    password required   pam_unix.so obscure sha512
    password required   pam_krb5.so use_authtok minimum_uid=1000
```

If you have multiple environments that you want to synchronize and you
don't want password changes to continue if the Kerberos password change
fails, use the `clear_on_fail` option.  For example:

```
    password required   pam_krb5.so clear_on_fail minimum_uid=1000
    password required   pam_unix.so use_authtok obscure sha512
    password required   pam_smbpass.so use_authtok
```

In this case, if `pam_krb5` cannot change the password (due to password
strength rules on the KDC, for example), it will clear the stored password
(because of the `clear_on_fail` option), and since `pam_unix` and
`pam_smbpass` are both configured with `use_authtok`, they will both fail.
`clear_on_fail` is not the default because it would interfere with the
more common pattern of falling back to local passwords if the user doesn't
exist in Kerberos.

If you use a more complex configuration with the Linux PAM `[]` syntax for
the session and account groups, note that `pam_krb5` returns a status of
ignore, not success, if the user didn't log on with Kerberos.  You may
need to handle that explicitly with `ignore=ignore` in your action list.

There are many, many other possibilities.  See the Linux PAM documentation
for all the configuration options.

On Red Hat systems, modify `/etc/pam.d/system-auth` instead, which
contains all of the configuration for the different stacks.

You can also use pam-krb5 only for specific services.  In that case,
modify the files in `/etc/pam.d` for that particular service to use
`pam_krb5.so` for authentication.  For services that are using passwords
over TLS to authenticate users, you may want to use the `ignore_k5login`
and `no_ccache` options to the authenticate module.  `.k5login`
authorization is only meaningful for local accounts and ticket caches are
usually (although not always) only useful for interactive sessions.

Configuring the module for Solaris is both simpler and less flexible,
since Solaris (at least Solaris 8 and 9, which are the last versions of
Solaris with which this module was extensively tested) use a single
`/etc/pam.conf` file that contains configuration for all programs.  For
console login on Solaris, try something like:

```
    login auth sufficient /usr/local/lib/security/pam_krb5.so minimum_uid=100
    login auth required /usr/lib/security/pam_unix_auth.so.1 use_first_pass
    login account required /usr/local/lib/security/pam_krb5.so minimum_uid=100
    login account required /usr/lib/security/pam_unix_account.so.1
    login session required /usr/local/lib/security/pam_krb5.so retain_after_close minimum_uid=100
    login session required /usr/lib/security/pam_unix_session.so.1
```

A similar configuration could be used for other services, such as ssh.
See the pam.conf(5) man page for more information.  When using this module
with Solaris login (at least on Solaris 8 and 9), you will probably also
need to add `retain_after_close` to the PAM configuration to avoid having
the user's credentials deleted before they are logged in.

The Solaris Kerberos library reportedly does not support prompting for a
password change of an expired account during authentication.  Supporting
password change for expired accounts on Solaris with native Kerberos may
therefore require setting the `defer_pwchange` or `force_pwchange` option
for selected login applications.  See the description and warnings about
that option in the pam_krb5(5) man page.

Some configuration options may be put in the `krb5.conf` file used by your
Kerberos libraries (usually `/etc/krb5.conf` or
`/usr/local/etc/krb5.conf`) instead or in addition to the PAM
configuration.  See the man page for more details.

The Kerberos library, via pam-krb5, will prompt the user to change their
password if their password is expired, but when using OpenSSH, this will
only work when `ChallengeResponseAuthentication` is enabled.  Unless this
option is enabled, OpenSSH doesn't pass PAM messages to the user and can
only respond to a simple password prompt.

If you are using MIT Kerberos, be aware that users whose passwords are
expired will not be prompted to change their password unless the KDC
configuration for your realm in `[realms]` in `krb5.conf` contains a
`master_kdc` setting or, if using DNS SRV records, you have a DNS entry
for `_kerberos-master` as well as `_kerberos`.

## Debugging

The first step when debugging any problems with this module is to add
`debug` to the PAM options for the module (either in the PAM configuration
or in `krb5.conf`).  This will significantly increase the logging from the
module and should provide a trace of exactly what failed and any available
error information.

Many Kerberos authentication problems are due to configuration issues in
`krb5.conf`.  If pam-krb5 doesn't work, first check that `kinit` works on
the same system.  That will test your basic Kerberos configuration.  If
the system has a keytab file installed that's readable by the process
doing authentication via PAM, make sure that the keytab is current and
contains a key for `host/<system>` where <system> is the fully-qualified
hostname.  pam-krb5 prevents KDC spoofing by checking the user's
credentials when possible, but this means that if a keytab is present it
must be correct or authentication will fail.  You can check the keytab
with `klist -k` and `kinit -k`.

Be sure that all libraries and modules, including PAM modules, loaded by a
program use the same Kerberos libraries.  Sometimes programs that use PAM,
such as current versions of OpenSSH, also link against Kerberos directly.
If your sshd is linked against one set of Kerberos libraries and pam-krb5
is linked against a different set of Kerberos libraries, this will often
cause problems (such as segmentation faults, bus errors, assertions, or
other strange behavior).  Similar issues apply to the com_err library or
any other library used by both modules and shared libraries and by the
application that loads them.  If your OS ships Kerberos libraries, it's