Re: cross-realm authentication problem
- From: Bjoern Tore Sund <bjorn.sund@xxxxxxxxx>
- Date: Fri, 29 May 2009 15:19:28 +0200
Douglas E. Engert wrote:
Bjoern Tore Sund wrote:I am trying to get cross-realm authentication to work between AD and our MIT Kerberos realm. Windows client are in KLIENT.UIB.NO, Windows user accounts are in UIB.NO, Unix/Linux machines and accounts are in UNIX.UIB.NO. User names in UIB.NO and UNIX.UIB.NO are the same.
So KLIENT.UIB.NO and UIB.NO are AD and UNIX.UIB.NO is MIT? What version?
Correct. Windows 2003 SP2 and MIT Kerberos 1.6.3.
KLIENT.UIB.NO and UIB.NO trust each other, UIB.NO and UNIX.UIB.NO have two-way trust enabled, transitive.
I have one web server running RHEL4, apache 2.0.52 and Kerberos 1.3.4 as provided by Redhat, self-compiled mod_auth_kerb 5.4, and another running RHEL5, apache 2.2.3 and Kerberos 1.6.1 as provided by Redhat, self-compiled mod_auth_kerb 5.4. krb5.conf, .htaccess etc are identical on the two web servers, both have principals in UNIX.UIB.NO.
From Unix/Linux machines with user authenticated in UNIX.UIB.NO Kerberos negotiation works fine. After choosing UNIX.UIB.NO as authentication domain on a Windows machine Kerberos negotiation works fine. After authenticating against UIB.NO on a Linux machine (which have UNIX.UIB.NO as primary realm in krb5.conf) cross-realm authentication works fine. But using a Windows machine where the user is authenticated in UIB.NO I get cross-realm authentication only to the web server running RHEL4, not the one running RHEL5, I never even get a ticket for UNIX.UIB.NO from AD when trying to access the RHEL5 server web page. The only difference between the RHEL4 and RHEL5 server should be the Kerberos and Apache versions.
default_realm = UNIX.UIB.NO
ticket_lifetime = 144h
forwardable = yes
proxiable = yes
permitted_enctypes = des3-hmac-sha1 des-cbc-crc rc4-hmac des-cbc-md5
default_tgs_enctypes = des-cbc-crc
default_tkt_enctypes = des-cbc-crc
dns_lookup_realm = true
dns_lookup_kdc = true
udp_preference_limit = 1
You should not need the capaths as the default it to assume
a hierarchical realm tree, which you have.
Ok. Didn't help to remove the whole capaths section either. :(
===
AuthType Kerberos
AuthName "Kerberos Login "
KrbMethodNegotiate on
KrbMethodK5Passwd off
KrbAuthRealms UNIX.UIB.NO
KrbServiceName "HTTP"
Krb5Keytab /etc/httpd/conf/radisson_http.keytab
KrbLocalUserMapping on
Require valid-user
===
Any ideas where I need to look to figure this one out? It looks as if the RHEL5 server somehow fails to inform the windows client that it needs to get a TGT for UNIX.UIB.NO, but why then does the RHEL4 server provide this information?
The server does not inform the client. The client figures out it needs
to do cross realm, and the KDC figures out what enctype to use for the
server. With Windows, the Microsoft client code asks its KDC for a
a referral. But you said both the web servers are in the same realm,
and lod one works and the new one does not.
I thought the web server was supposed to use the www-authenticate: header not only to say that it supports Negotiate authentication but also which realm to negotiate with. That was defined in HTTP 1.0 but I haven't found it for 1.1. And indeed, neither of the two web servers use this field for that. In fact, the http headers are identical except for the apache version:
HTTP/1.1 401 Authorization Required
Date: Fri, 29 May 2009 12:12:53 GMT
Server: Apache/2.0.52 (Red Hat)
WWW-Authenticate: Negotiate
WWW-Authenticate: Basic realm="Kerberos Login"
Content-Length: 401
Content-Type: text/html; charset=iso-8859-1
The first www.authenticate is added by KrbMethodnegotiate being on, the second by krbmethodk5passwd being on. I can't figure out how the client figures out which realm to get a TGT for and then request a service ticket from without the HTTP header specifying this. On the linux clients and servers I set a specific mapping from dns domain .uib.no to realm UNIX.UIB.NO, is there a way to do this on Windows?
krb5-1.6.1 supports RC4 and DES (plus others).
Windows 2003 only supports RC4 and DES.
krb5-1.3.1 only supports DES.
So there might be some enctype issue were RC4 is being used.
Does the keytab file for the RHEL have a RC4 and/or DES key?
Entry for principal HTTP/radisson.uib.no with kvno 4, encryption type Triple DES cbc mode with HMAC/sha1 added to keytab WRFILE:/tmp/radisson_http.keytab.
Entry for principal HTTP/radisson.uib.no with kvno 4, encryption type DES cbc mode with CRC-32 added to keytab WRFILE:/tmp/radisson_http.keytab.
Entry for principal HTTP/radisson.uib.no with kvno 4, encryption type ArcFour with HMAC/md5 added to keytab WRFILE:/tmp/radisson_http.keytab.
I'd understand that if it was the RHEL4 machine I couldn't talk to.
Wireshark on the client can be very helpful, as you can see
all the Krb5 requests and responses including enctypes.
The KDC may be sending some error messages or sending a key
with an enctype that is not in the keytab.
http://www.wireshark.org/
When trying to retrieve the web page from the RHEL5 server there is no attempt to contact a KDC at all.
-BT
--
Bjørn Tore Sund Phone: 555-84894 Email: bjorn.sund@xxxxxxxxx
IT department VIP: 81724 Support: http://bs.uib.no
Univ. of Bergen
When in fear and when in doubt, run in circles, scream and shout.
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