Paranoid Penguin - Single Sign-On and the Corporate Directory, Part II

Ti Leggett continues his series on building a secure corporate directory.



for the different rights, you'll enable those users in the ldap-admins group to be administrators on that machine. These rights are different from sudo privileges, which are defined in /etc/sudoers. These rights control rights to tasks such as installing software and modifying system preferences.

At this point we should be able to log in as user leggett. Tiger's sshd supports both GSSAPI mechanisms, gssapi and gssapi-with-mic. Previous OS X versions supported only gssapi, so a password was required when logging in to or from an OS X client. SSO support is enabled out of the box for sshd, so there's no config files to edit.

As I stated earlier, with v10.4, almost all of OS X's built-in services and applications are Kerberized, including Apple's If you're running your own CA or using self-signed certificates, you need to import your CA's certificate into the System keychain first, so won't complain when connecting to self-signed SSL-enabled services like IMAP and SMTP. Copy the CA cert to the OS X client and then run certtool:

sudo certtool i ci-cert.pem v \

Now you're ready to start The trick to enabling GSSAPI during the account creation process is to fill in the user name and leave the password blank. If you don't already have valid credentials, it will prompt you for your Kerberos password. Once the account is created, go back and enable SSL for IMAP. By default it's not enabled, and doesn't give you the choice at account creation time.

All versions of OS X since v10.3 ship with a GUI application for managing Kerberos credentials named (Figure 4), but it's buried in /System/Library/CoreServices. You can add this useful app to your dock and have it start at boot. It can automatically renew your credentials when they're expiring and easily show you how much longer your credentials are valid, among other useful features.

Figure 4. OS X Kerberos Application

Many of Apple's services and applications are fully Kerberized, including Safari, VPN, Xgrid and AFP, making your Apple users and administrators first-class citizens in your network.

Wrapping Up

By now you're probably starting to realize the enormous potential of LDAP directories and Kerberos authentication. You have a powerful and scalable infrastructure as well as clients making full use of it. In my next article, we'll discuss how to integrate in one more type of client, Microsoft Windows. Until then, enjoy the fruits of your labor!


This work was supported by the Mathematical, Information, and Computational Sciences Division subprogram of the Office of Advanced Scientific Computing Research, Office of Science, U.S. Department of Energy, under Contract W-31-109-ENG-38. Additional support has been provided by the Computation Institute at the University of Chicago and the National Science Foundation under Grant SCI: 0451491.

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Ti Leggett ( is a systems administrator for the Futures Laboratory of the Mathematics and Computer Science Division at Argonne National Laboratory. He also has a joint appointment with the Computation Institute at the University of Chicago.