Testing macOS Catalina Kerberos SSO Extension Over VPN


Enabling the off-network Kerberos Single Sign-On Experience.

Working at VMware, I’m surrounded by great technology and super-smart folks! In our portfolio of technologies, the folks in our R&D have recently been putting quite a bit of effort into building out macOS capabilities for our Workspace ONE Tunnel client for macOS. Workspace ONE admins can leverage the same VMware technology they used to enable per-app VPN for iOS and Android, but now on macOS! There’s a bit of nuance to configuring the VPN client if you’re previously familiar with iOS (look for my Operational Tutorial soon to hit TechZone). That said, the premise is the same – by configuring the appropriate rules, the Tunnel app redirects traffic from whitelisted applications back into your network through the Unified Access Gateway.

Sounds simple enough, right? So a few of us wondered if we could leverage some of this new technology with new Kerberos SSO Extension in macOS Catalina.

Use-Cases

Sitting down to plan out testing, there were four main use cases I hoped to prove out:

  1. What if the new Kerberos SSO Extension in macOS Catalina was just another one of those applications that you redirected over a VPN?
  2. Could you, in theory, get Kerberos Tickets to an unbound Mac to use for authenticating to Workspace ONE Access and/or internal websites (over Per-App VPN)?
  3. Could you also leverage the Kerberos SSO Extension to sync your local (non-mobile) macOS User account’s password with the on-prem AD password over Per-App VPN?
  4. Could you change your on-prem AD password remotely over Per-App VPN when it neared the expiration date?

It seemed pretty straightforward… but NOPE! I ran into quite a bit of unexpected behavior! Luckily, one of my coworkers, Adam, had a slightly different configuration than I and was able to test all of this as functioning for macOS that is on-network with on-premise Active Directory.

Test Environment Configuration

Here’s how I have things configured in my test environment:

  • Isolated Network with the following VMs:
    • Two Windows Server 2016 Domain Controllers, one of which runs DNS
    • Airwatch Cloud Connector and Workspace ONE Access Connnectors configured
    • One IIS web server running two sites – one configured for Kerberos Auth and one configured for Anonymous access.
    • One ADCS server (not used for this testing)
  • Unified Access Gateway Appliance v3.8 (the only VM with inbound access from the Internet)
    • Tunnel/Edge service is enabled/configured
  • SaaS-based Workspace ONE UEM and Workspace ONE Access.
  • Workspace ONE Tunnel for macOS configured as an auto-deployed Volume Purchase app (from Apple Business Manager)
  • The DNS name for my AD domain set up in Device Traffic Rules for tunneling.
  • Google Chrome, Firefox, and Safari all configured to allow kerberos authentication to the website.

Commands

defaults write -g GSSDebugLevel 20

defaults write -g KerberosDebugLevel 20

log stream --debug --predicate '(subsystem == "com.apple.Heimdal") OR (subsystem == "com.apple.AppSSO") OR (subsystem == "org.h5l.gss") OR (subsystem == "com.apple.network") OR (process == "VMware Tunnel") '

Results

As it turns out, the Kerberos SSO Extension in Catalina appears designed for situations where macOS is on-network with an on-premise Active Directory. I went through some testing using our Per-App Tunnel (and a full-device Global Protect VPN), and ran into the following testing results:

Testing Item Per-App VPN (Tunnel) GlobalProtect (VPN)
Kerberos Ticket Obtained over VPN Yes! Yes!
Password Expiration Date Correct No! No!
Extension Detects local PW different from AD No! Yes!
User Change AD Password via Extension over VPN No! No!

I was able to confirm that a kerberos ticket is obtained using klist in Terminal. I could also confirm that I could authenticate to the Kerberos-enabled IIS website without having to provide a username/password in the browser. Kerberos functionality appeared to be working, just not any other functionality.

Looking Forward

I used Apple’s Feedback Assistant app to provide feedback to Apple and provided them with an environment to reproduce the issue. I’m hopeful that they can find a fix or provide some guidance to enabling the entirety of the Kerberos SSO Extension’s functionality over a VPN.

| Please reach out if you’ve done testing as well - I’d love to hear your experience!

More to come…

macOS  SSO  VPN 

See also