Provided by: inn2_2.5.2+20110413-1_i386 bug

NAME

       auth_krb5 - nnrpd Kerberos v5 authenticator

SYNOPSIS

       auth_krb5 [-i instance]

DESCRIPTION

       This program does authentication for nnrpd against a Kerberos v5 KDC.
       This is NOT real Kerberos authentication using service tickets;
       instead, a username and password is used to attempt to obtain a
       Kerberos v5 TGT to confirm that they are valid.  As such, this
       authenticator assumes that nnrpd has been given the user's username and
       password, and therefore is not as secure as real Kerberos
       authentication.  It generally should only be used with NNTP over TLS to
       protect the password from sniffing.

       Normally, you do not want to use this authenticator.  Instead, use
       ckpasswd with PAM support and configure the nnrpd PAM stack to use a
       Kerberos PAM module.  A full Kerberos PAM module is more sophisticated
       about how it validates passwords and has a much broader array of
       options than this authenticator.

OPTIONS

       -i instance
           If this option is given, instance will be used as the instance of
           the principal received from nnrpd and authentication will be done
           against that principal instead of the base principal.  In other
           words, a principal like "user", when passed to auth_krb5 invoked
           with "-i nntp", will be transformed into "user/nntp" before
           attempting Kerberos authentication.

           Since giving one's password to nnrpd is not as secure as normal
           Kerberos authentication, this option supports a configuration where
           all users are given a separate instance just for news
           authentication with its own password, so their regular account
           password isn't exposed via NNTP.

EXAMPLE

       The following readers.conf(5) fragment tells nnrpd to authenticate
       users by attempting to obtain Kerberos v5 TGTs for them, appending an
       instance of "nntp" to usernames before doing so:

           auth kerberos {
               auth: "auth_krb5 -i nntp"
           }

           access kerberos {
               users: "*/nntp"
               newsgroups: example.*
           }

       Access is granted to the example.* groups for all users who
       successfully authenticate.

BUGS

       Currently, any username containing realm information (containing "@")
       is rejected.  This is to prevent someone from passing in a username
       corresponding to a principal in another realm that they have access to
       and gaining access to the news server via it.  However, this is also
       something that people may wish to do under some circumstances, so there
       should be a better way of handling it (such as, perhaps, a list of
       acceptable realms or a -r flag specifying the realm in which to attempt
       authentication).

       It's not clear the right thing to do when the username passed in
       contains a "/" and -i was also given.  Right now, auth_krb5 will create
       a malformed Kerberos principal with multiple instances and attempt to
       authenticate against it, which will fail but perhaps not with the best
       error message.

HISTORY

       Originally written by Christopher P. Lindsey.  This documentation was
       written by Russ Allbery <rra@stanford.edu> based on Christopher's
       original README file.

       $Id: auth_krb5.pod 8595 2009-08-21 08:29:26Z iulius $

SEE ALSO

       ckpasswd(8), nnrpd(8), readers.conf(5).

       The latest version of Christopher's original nnrpkrb5auth may be found
       on his web site at <http://www.mallorn.com/tools/>.