I know a lot of people have run into this problem. I too had it occur. One of our guys here at the office guessed, correctly, that Centrify might be the problem. If you use Centrify, then here's what we did, which essentially uninstalls centrify. After you get past the login then the new centrify compatible with high sierra can be installed.
I am assuming these commands came from centrify.
Boot into single user mode (Command-S) and once you are at the terminal, run the following:
1. # mount -uw
2. # adleave -f
3. # /usr/local/share/centrifydc/bin/uninstall.sh
4. # mv /var/db/auth.db /var/db/auth.db.bak
5. Reboot your Mac
6. Login using local administrator account
NOTE - #rm /var/db/.AppleSetupDone may be needed between step 4-5
In my case, I ended up with keychain problems and a loop about repairing applications, which I am still working with Apple support to resolve, but at least it is not a reformat disk next step, which Apple suggested.