Hi,
First, enable SSH globally:
config sys set ssh enable true
Then, you can configure a local password for a specific user:
config cli password
Or do RADIUS authentication:
config radius server create x.x.x.x secret ****** acct-port 1813
config radius enable true
And configure your RADIUS server accordingly.
If your SSH authentication works, don't forget to disable the telnet service:
config sys set telnet enable false
Goodluck!