Monitor Remote System Clock Via HTTP Headers

Shibboleth authentication via simpleSAMLphp broke on one of our apps when the system clock on the Shibboleth server drifted more than a minute into the future.

I am not the administrator of the Shibboleth server. But it occured to me that even with no shell access to the server, I could detect clock drift by examining the time stamp in the HTTP headers from the server.

So, I wrote a Node script to use in a crontab to monitor the remote server’s clock accuracy.