[SOLVED] RE: [External] - Re: Issues getting Kerberos to work with realmd and Active Directory

[Wesley Taylor]

Thank you all for your responses. Fortunately for me, just running klist and 
picking the UPN form got me past this issue, but if I run into any issues in 
the future I will employ those other solutions. I appreciate the help!

-Wes


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-----Original Message-----
From: Simo Sorce <simo at redhat.com>
Sent: Thursday, July 30, 2020 12:33 PM
To: Wesley Taylor <wesley.taylor at numerica.us>; kerberos at mit.edu
Subject: [External] - Re: Issues getting Kerberos to work with realmd and 
Active Directory

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Wesley,
when joining hosts to AD a computer account is created and a UPN and SPNs are 
set on it.
Unlike MIT kerberos in AD heavy use of aliases is employed so each host have a 
"host password/key" that is shared with all the aliases created.
Most notably there are the UPN, generally of the form computername$@REALM and 
the SPNs which are a large number of service/fqdn at REALM principal names.

The important part here is that while you can get tickets for any of those 
names (the KDC has many canonicalization rules that will also match in a 
case-insensitive way) when you ask for a TGT (the kinit
operation) AD normally will accept a request only if the UPN form is used as 
the client principal and will refuse other forms (even though the key is the 
same).

realmd has an option to specify what to set the UPN to to change the default 
AD behavior. (See the --user-principal option in realm.8 manpage). You can use 
it to control what to use at join time, then you should be able to use exactly 
that name to kinit from the generated keytan.

HTH,
Simo.

On Thu, 2020-07-30 at 17:00 +0000, Wesley Taylor wrote:
> Hi All,
>
> I am trying to get HTCondor with Kerberos authentication (
> https://usg02.safelinks.protection.office365.us/?url=https%3A%2F%2Fhtc
> ondor.readthedocs.io%2Fen%2Fstable%2Fadmin-manual%2Fsecurity.html%3Fhi
> ghlight%3DKerberos%23kerberos-authentication&amp;data=02%7C01%7C%7Cbb5
> bd43850e34b17771508d834b70953%7Cfae7a2aedf1d444e91bebabb0900b9c2%7C0%7
> C0%7C637317308723651795&amp;sdata=uYxqJbuTqP8JbYm8Qx4oZjyGKhI1hTVWkAYH
> IKooivI%3D&amp;reserved=0
> ) to work on some linux machines I have which I joined to Windows
> Active Directory with realmd. HTCondor tries to authenticate with the
> machine principal, but I am having a hard time figuring out what that
> is. When I run 'klist -k' I see a bunch of entries from
> /etc/krb5.keytab along the lines of host/fqdn at REALM. However, when I
> run 'kinit -k' I get "kinit: Client $(hostname) not found in Kerberos
> database".
>
> I then interrogated the realm with adcli, using 'adcli testjoin -- 
> verbose' and it outputs the computer account name as
> HOST/HOSTNAME at REALM. When I run 'kinit -k HOST/HOSTNAME at REALM' I get
> back the error "kinit: Keytab contains no suitible keys for
> HOST/HOSTNAME at REALM".
>
> I am confused because when I run 'adcli update --verbose' it says it
> updated the keytab at /etc/krb5.keytab and outputs the same account
> name (which I am assuming is the principal for the computer) as adcli
> testjoin. I am really scratching my head about this, what am I doing
> wrong here?
>
> Thanks,
> Wes
>
>
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--
Simo Sorce
RHEL Crypto Team
Red Hat, Inc



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