Mac OS X Server: Unable to add the root user to service-based ACL for SSH

Issue or symptom

When using a service-based Access Control List (ACL) for ssh services, you may be unable to add the root user to the list of allowed users.

Solution

Add the root user to the ACL using niutil in Terminal.

1. Open Terminal
2. Execute this command on a single line
   
   sudo dseditgroup -o edit -a root -t user com.apple.access_ssh