I want to set my firewall to only allow HTTP connections that originate from Apps Script. My Google Spreadsheets project uses URLFetch make queries back to my server. For development, that "server" is just my desktop at home. To allow that, I had to set a rule in the firewall to allow TCP on port 80. Restricting source address is never a substitute for real security, but it would block most of the scripts that periodically scan my IP for IIS/Apache vulnerabilities. So far, the legitimate connections are coming from 18.104.22.168. Presumably, that could change at any time. I can't get reverse DNS on that (i.e., "host 22.214.171.124") so I can't even do much weaker programmatic filtering.
Is there a known IP address range that Apps Script sends URLFetch connects from?
Alternate suggestions are also welcome. Unfortunately, App Engine won't work. It's not compatible with my application.