Then log in as admin to Nodegrid WebUI, and go to System :: Toolkit :: System Certificate.
Upload the certificate file in .pem or .crt extension by selecting Local Computer or Remote Server.
If applying via CLI, the only option is via remote server (Local Computer is not available).
Log in as admin via console or ssh, then type:
[admin@nodegrid /]# cd /system/toolkit/
[admin@NewYork-DC toolkit]# system_certificate
[admin@nodegrid {toolkit}]# set from=remote_server
[admin@nodegrid {toolkit}]# set url=<PROTOCOL>://<ServerAddress>/<Remote File>
[admin@nodegrid {toolkit}]# set username=<username>
[admin@nodegrid {toolkit}]# set password=<password>
[admin@nodegrid {toolkit}]# commit