Here is the file at:
/usr/lib/systemd/system/sssd.service
[Unit]
Description=System Security Services Daemon
# SSSD will not be started until syslog is
After=syslog.target
[Service]
ExecStart=/usr/local/sbin/sssd
# These two should be used with traditional UNIX forking daemons
# consult systemd.service(5) for more details
Type=forking
PIDFile=/usr/local/var/run/sssd.pid
[Install]
WantedBy=multi-user.target
Then it's just:
systemd enable sssd