Recently I was attempting to execute an explicit OAuth2.0 flow for the StackExchange API within a Google Apps script, and ran into a problem. At step 4 of the process, my POST request for an access token consistently resulted in a 404 error.
I tested the same code outside of Apps Script (using a simple curl command) and received an access token without an issue. In addition, requests to the StackExchange API that don't require auth can be conducted within Apps Script without error.
I am wondering if the auth requests coming from google.com are being rejected to prevent accidental crawling (or for some other reason). If this is the case, would it be possible to allow requests coming from script.google.com? This would allow Apps Script users to make full use of the API.