There are situations when an IT systems provider (like Managed Services, or Systems Integration and alike) has by contract restricted access to the resources supporting their products and the client demands such a SLA that must be monitored, but does not provide the ways or resources to assess it, to check it or to monitor it. Neither basic stuff like public keys to make an automatic SSH connection, just the interactive shell itself (maybe you are lucky and have granted a VPN access!)
If this is your case, you can count on the GetPW, an Open Source software project designed to support Nagios monitoring on remote systems with just a SSH interactive shell connections. With GetPW you can start jobs via SSH by Nagios, without having to put user and passawords in clear-text inside configuration files. You have them safely stored together their mandatory information of hosts and services on a MySQL database that can be safely retrieved to accomplish your needs and comply with your agreed SLA.