So there must be a more convenient way to configure kerberos. If only I had some way to pull the information of the current KDC from the domain-data. But wait – there is DNS. There are a couple of service-entries in DNS to point to all available kerberos servers in the domain! That sounds promising.

So I changed my krb5.conf file and added

dns_lookup_realm = yes
dns_lookup_kdc = yes

to the libdefaults section. Then I removed the realms and domain_realms section. Now all information about available KDC servers is directly pulled from DNS – sweet.

While the basic setup is somewhat unchanged, only the file core/authentication_api.php needs to be changed. The login.php doesn’t need to be changed anymore, since the functionallity moved to the authentication_api.php.

I added an updated patchfile to apply the necessary changes to the file.

Update: a new post is availbe, with an updates patchfile for Mantis 1.2.1!

The more tools are being used in an enterprise environment, the more logins and passwords need to be memorized. A first step is to use LDAP based authenticatin. In MS Windows based networks this offers to ability to manage all users in the Active Directory, so the users only have to use on username/password. But the user will still have to enter this into a login-screen in order to access the application.

Using SSO the user is always identified by already existind credentials. In the best case, the logon credetials of the operating system are being used. Since Active Directory is based on the Kereberos authentication protocoll, this offers the ability to use kerberos based authentication in other applications, and thus re-using the existing windows authentication.

The Internet Explorer is capable of using the windws logon-credentials to authenticate users on certain webservers. But with a slight modification this can also be used on an Apache running on a linux box. How to setup Apache to allow kerberos authentication is explained in another article. Once Apache is setup correct, Mantis needs to be slightly modified to use the information supplied by the kerberos authentication. My modifications are all based on the current development-release of mantis 1.1.0a2.

Modifing Mantis

Basically three files need to be modified: core\authentication_api.php, login.php and config.inc.php.

1. In config.inc.php I switch from LDAP authentication to HTTP_AUTH, since I wand the webserver to handle the authentication. Also I introduce a new configuration setting sso_user_regex. This is needed, because I need to extract the username from the user identified by the webserver. So I use this handy little regex to do this for me:

            $g_login_method    = HTTP_AUTH;
            $g_sso_user_regex  = '/^(.*)@ACME\.COM$/i';

   This regex would extract the username portion for users of the domain “ACME.COM”.

2. Next would be to modify login.php to extract the username from the authenticated user, if the user was detected using “Negotiation” (which is the case if IWA was used). So I apply my previously defined regex to the “Remote-User” variable of the server to get my mantis username. So we have to insert some code at line 32:

         if ( isset($_SERVER['REMOTE_USER'])) { #  $_SERVER['AUTH_TYPE'] == 'Negotiate' )
           preg_match(config_get('sso_user_regex'), $_SERVER['REMOTE_USER'], $user_match);
           $f_username = $user_match[1];
         }

3. The last step is to add an additional condition to the authentication_api.php to prevent from trying to authenticate the user with the mantis user database using the username and password. This would only work, if the username and password would be supplied by the webserver, but using IWA we only have the username (the password is not transmitted in IWA, only the logon-challange). So this would only work if Basic Authentication would be used instead of kerberos authentication. So validating username and password with the mantis user database is restricted for HTTP_AUTH by modifing line 121:

         if ( HTTP_AUTH != $t_login_method && !auth_does_password_match( $t_user_id, $p_password ) ) {
         # if ( !auth_does_password_match( $t_user_id, $p_password ) ) {

So this should be all, to get Integrated Windows Authentication running. Below is a patchfile to apply the changes of authentication_api.php and login.php.

Attached you’ll find a patch-file to modified the corresponding files. To apply the patch you simple need to execute (assuming you have patch, and you’re executing it within your install-directory of Mantis):

   patch < iwa_sso.patch -p0

Download: iwa_sso patch

First of all the mod_auth_kerb is needed to add kerberos capabilities to Apache. Besides this a working configuration of kerberos 5 is needed on the server running Apache.

Prepare Active Directoy

1. To enable authentication against Active Directory a dedicated user is needed for each Apache server. The password doesn’t really matter, but the username should use a certain convention and maybe a explaining description. Such a account could be http-linuxserver.
2. For the newly created account a keytab is needed to use the account from Apache. To create such a keytab the ktpass.exe is needed. The command on a Server running Windows 2003 looks like this:

            ktpass.exe -princ HTTP/linuxserver@ACME.COM
            -mapuser http-linuxserver
            -crypto DES-CBC-MD5 +DesOnly
            -pass myverygoodpass
            -ptype KRB5_NT_PRINCIPAL
            -out linuxxserver.keytab

   For domain-controllers running Windows 2000 the command might be slightly different.

Configuring Apache

After installing the mod_auth_kerb a couple configuration settings need to be made.

1. First the previously created keytab file needs to be copied to the server (prefferedly using scp or simillar).
2. Change to owner of the keytab-file to the user running Apache (depending on your distribution that could be apache, www-data or something else).
3. To secure a directory or using kerberos the following entries need to be added to the appropriate configuration section of apache:

       AuthType Kerberos
       AuthName "Kerberos Login"
       KrbServiceName HTTP
       KrbMethodK5Passwd On
       KrbAuthRealms ACME.COM
       Krb5KeyTab /etc/httpd/conf/linuxserver.keytab
       require valid-user

4. Restart Apache to apply the changes.

If you now access the secured website using Internet Explorer that supports Integrated Windows Authentication, you can see the content without being prompted for a password as long as you have valid windows-credentials.

 hash -p /pfad/zu/meinem/programm/programm kurzname

Anhand unseres Beispiels sieht das so aus:

 hash -p /home/ichselber/test/fiessesskript.sh fies

Mit diesem Befehl bewirken Sie, dass ab jetzt die Eingabe fies reicht. Wenn Sie nur hash eingeben, bekommen Sie die Liste der bereits gespeicherten Kommandos angezeigt. Mit dem Befehl hash -r wird die Liste geleert.

Voraussetzungen

Folgende Packages sollten installiert sein:

• winbind
• samba
• libkrb53
• krb5-user

Bei der Installation von krb5-conf werden ein paar Informationen direkt abgefragt, wie etwas der Default Realm (entspricht dem Namen der Active Directory Domäne) und des Domänenservers. Anschließend sollte allerdings die Datei /etc/krb5.conf noch ein wenig bearbeitet werden. Soll Kerberos nur für in Zusammenhang mit Winbind eingesetzt werden, so können die ganzen MIT-Realms ersteinmal entfernt werden. Auch werden eine ganze Reihe von Einstellungen für Kerberos 4 nicht benötigt; auch diese können weg.

Eine einfache krb5.conf Datei für die Domäne ACME.COM (aka Realm) könnte also so aussehen:

 [libdefaults]
        default_realm = ACME.COM
        kdc_timesync = 1
        ccache_type = 4
        forwardable = true
        proxiable = true
 [realms]
 ACME.COM = {
        kdc = server.acme.com
        admin_server = server.acme.com
 }
 [domain_realm]
        acme.com = ACME.COM
        .acme.com = ACME.COM

Damit die Benutzerauflösung auch durch Winbind erfolgen kann, muss zum einen in der nsswitch.confneben compat auch windbind eingetragen werden (auf diese Weise werden sowohl lokale Benutzer als auch Benutzer über Winbind zur Verfügung gestellt) und Samba muss noch so eingestellt werden, daß die Authentifizierung über das ADS läuft. Eine einfach smb.conf sieht dann etwa so aus:

 # Global parameters
 [global]
        workgroup = ACME
        realm = ACME.COM
        idmap uid = 10000-20000
        idmap gid = 10000-20000
        winbind separator = /
        winbind use default domain = yes
        server string = %h server (Samba %v)
        security = ADS
        password server = server.acme.com
        client use spnego = yes

Damit die Änderungen übernommen werden, muss sowohl Samba als auch Winbind neu gestartet werden (/etc/init.d/samba restart; /etc/init.d/winbind restart). Anschließend kann mit wbinfo -u eine Liste alle Benutzer über winbind angezeigt werden.

Nun sollten sich auch Windows-Benutzer, die auf dem Linux Rechner nicht lokal angelegt sind, auf Samba-Freigaben verbinden können. Die Authentifizierung wird im Hintergrund durch Winbind erledgit.