AUTH_KRB5(8)

💅 NAME 💅

ok so like, auth_krb5 — the nnrpd Kerberos v5 authenticator. that's the whole vibe. it's the Kerberos v5 authenticator for nnrpd, bestie, and we're gonna get into it 💖

this is a page from the InterNetNews Documentation, and it's literally all about one little program. buckle up 🎀

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✨ SYNOPSIS ✨

auth_krb5 [-i instance]

that's it. that's the whole synopsis. iconic. 🫶

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🌸 DESCRIPTION 🌸

okay so here's the tea ☕ — this program does authentication for nnrpd against a Kerberos v5 KDC.

but now, important plot twist: this is NOT real Kerberos authentication using service tickets. nope, nope, nope 🙈 instead, a username and password is used to attempt to obtain a Kerberos v5 TGT to confirm that they are valid. so like, it's doing the most to check your creds are real, but it's not doing it the fancy Kerberos way 😭

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. bestie please hear me on this one — it generally should only be used with NNTP over TLS to protect the password from sniffing. no plaintext passwords out here, periodt 💀

and honestly? normally, you do not want to use this authenticator. like, at all. 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. it's giving "the glow-up version" honestly 👑

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🦋 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. the way that transformation happens?? so clean ✨

okay so why does this option even exist — 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. protecting the main character's real password?? we stan 💜

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🎀 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.*
}

and the result? access is granted to the example.* groups for all users who successfully authenticate. slay 💖

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🤔 BUGS 🤔

ok so there's some caveats and i'm gonna be so fr fr with you:

• 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. but — and this is the messy part — 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). so like, it's a known thing, and it's fine, but it's not fine 😭
• 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. so it'll fail, but the error message is gonna be kinda mid. ngl that's a little embarrassing 🙈

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👑 HISTORY 👑

originally written by Christopher P. Lindsey. this documentation was written by Russ Allbery <eagle@eyrie.org> based on Christopher's original README file. giving credit where credit is due, we love to see it 🫶

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🌈 SEE ALSO 🌈

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

go read those too, iykyk 💅

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and that's the whole page bestie!! 💖 this one's from INN 2.7.4, dated 2022-07-10 — so it's got a little vintage energy but it's still serving ✨ stay secure, use TLS, and don't hand your password to strangers 🎀