Provided by: inn2_2.6.5-1_amd64 bug


       auth_krb5 - nnrpd Kerberos v5 authenticator


       auth_krb5 [-i instance]


       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.


       -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.


       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.


       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.


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


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