=head1 NAME

ckpasswd - nnrpd password authenticator

=head1 SYNOPSIS

B<ckpasswd> [B<-gs>] [B<-d> I<database>] [B<-f> I<filename>]
[B<-u> I<username> B<-p> I<password>]

=head1 DESCRIPTION

B<ckpasswd> is the basic password authenticator for nnrpd, suitable for
being run from an auth stanza in I<readers.conf>.  See readers.conf(5) for
more information on how to configure an nnrpd authenticator.

B<ckpasswd> accepts a username and password from nnrpd and tells nnrpd(8)
whether that's the correct password for that username.  By default, when
given no arguments, it tries to check the password using PAM if support
for PAM was found when INN was built.  Failing that, it tries to check the
password against the password field returned by getpwnam(3).  Note that
these days most systems no longer make real passwords available via
getpwnam(3) (some still do if and only if the program calling getpwnam(3)
is running as root).

Note that B<ckpasswd> expects all passwords to be stored encrypted by the
system crypt(3) function and calls crypt(3) on the supplied password
before comparing it to the expected password (when using any method other
than PAM).

=head1 OPTIONS

=over 4

=item B<-d> I<database>

Read passwords from a database (ndbm or dbm format depending on what your
system has) rather than by using getpwnam(3).  B<ckpasswd> expects
I<database>.dir and I<database>.pag to exist and to be a database keyed by
username with the encrypted passwords as the values.

While INN doesn't come with a program intended specifically to create such
databases, on most systems it's fairly easy to write a Perl script to do
so.  Something like:

    #!/usr/bin/perl
    use NDBM_File;
    use Fcntl;
    tie (%db, 'NDBM_File', '/path/to/database', O_RDWR|O_CREAT, 0640)
        or die "Cannot open /path/to/database: $!\n";
    $| = 1;
    print "Username: ";
    my $user = <STDIN>;
    chomp $user;
    print "Password: ";
    my $passwd = <STDIN>;
    chomp $passwd;
    my @alphabet = ('.', '/', 0..9, 'A'..'Z', 'a'..'z');
    my $salt = join '', @alphabet[rand 64, rand 64];
    $db{$user} = crypt ($passwd, $salt);
    untie %db;

Note that this will echo back the password when typed; there are obvious
improvements that could be made to this, but it should be a reasonable
start.  Sometimes a program like this will be available with the name
B<dbmpasswd>.

This option will not be available on systems without dbm or ndbm
libraries.

=item B<-f> I<filename>

Read passwords from the given file rather than using getpwnam(3).  The
file is expected to be formatted like a system password file, at least
vaguely.  That means each line should look something like:

    username:pdIh9NCNslkq6

(and each line may have an additional colon after the encrypted password
and additional data; that data will be ignored by B<ckpasswd>).  Lines
starting with a number sign (`#') are ignored.  INN does not come with a
utility to create the encrypted passwords, but B<htpasswd> (which comes
with Apache) can do so and it's a quick job with Perl (see the example
script under B<-d>).  If using Apache's B<htpasswd> program, be sure to
give it the B<-d> option so that it will use crypt(3).

=item B<-g>

Attempt to look up system group corresponding to username and return a
string like "user@group" to be matched against in F<readers.conf>.  This
option is incompatible with the B<-d> and B<-f> options.

=item B<-p> I<password>

Use I<password> as the password for authentication rather than reading a
password using the nnrpd authenticator protocol.  This option is useful
only for testing your authentication system (particularly since it
involves putting a password on the command line), and does not work when
B<ckpasswd> is run by B<nnrpd>.  If this option is given, B<-u> must also
be given.

=item B<-s>

Check passwords against the result of getspnam(3) instead of getpwnam(3).
This function, on those systems that supports it, reads from /etc/shadow
or similar more restricted files.  If you want to check passwords supplied
to nnrpd(8) against system account passwords, you will probably have to
use this option on most systems.

Most systems require special privileges to call getspnam(3), so in order
to use this option you may need to make B<ckpasswd> setgid to some group
(like group "shadow") or even setuid root.  B<ckpasswd> has not been
specifically audited for such uses!  It is, however, a very small program
that you should be able to check by hand for security.

This configuration is not recommended if it can be avoided, for serious
security reasons.  See L<readers.confZ<>(5)/SECURITY CONSIDERATIONS> for
discussion.

=item B<-u> I<username>

Authenticate as I<username>.  This option is useful only for testing (so
that you can test your authentication system easily) and does not work
when B<ckpasswd> is run by B<nnrpd>.  If this option is given, B<-p> must
also be given.

=back

=head1 EXAMPLES

See readers.conf(5) for examples of nnrpd(8) authentication configuration
that uses B<ckpasswd> to check passwords.

To test to make sure that B<ckpasswd> is working correctly, you can run it
manually and then give it the username (prefixed with C<ClientAuthname:>)
and password (prefixed with C<ClientPassword:>) on standard input.  For
example:

    (echo 'ClientAuthname: test' ; echo 'ClientPassword: testing') \
        | ckpasswd -f /path/to/passwd/file

will check a username of C<test> and a password of C<testing> against the
username and passwords stored in F</path/to/passwd/file>.  On success,
B<ckpasswd> will print C<User:test> and exit with status 0.  On failure,
it will print some sort of error message and exit a non-zero status.

=head1 HISTORY

Written by Russ Allbery <rra@stanford.edu> for InterNetNews.

$Id: ckpasswd.pod,v 1.6.2.2 2003/08/08 22:02:42 vinocur Exp $

=head1 SEE ALSO

readers.conf(5), nnrpd(8)

=cut
