To check whether GSSAPI(SSO) works or not, you need to enter the command in your Ubuntu server:
Point 2.4 from my guide
kinit -V -k -t /usr/share/openfire/resources/openfire.keytab xmpp/srv-chat.domain.local@DOMAIN.LOCAL
If everything works correctly, a record should appear:
Authenticated to Kerberos v5
Look at my two screenshots from two Openfire servers (First server on Ubuntu 16.04 and second server on Ubuntu 18.04)
