I currently have App Engine up and running, protected by IAP, and my eventual aim is to have this be triggered by an Apps Script project. I've tested the code without IAP and it works fine. However, I'm running into difficulties successfully authorizing access to it when IAP is enabled.
I've added myself as an IAP-secured Web App User (as well as Policy Admin) to the App Engine, but whenever I try triggering it from a GSheets Apps Script where I'm the owner and it's associated with the correct GCP project (using this great explanation as a guide) I get the following:
"Invalid IAP credentials: JWT audience doesn't match this application ('aud' claim (1084708005908-bk66leo0dnkrjsh276f0rgeoq8ns87qu.apps.googleusercontent.com) doesn't match expected value (1084708005908-oqkn6pcj03c2pmdufkh0l7mh37f79po2.apps.googleusercontent.com))"
I've tried adding/removing various permissions to my account, as well creating a new Apps Script and re-adding to the project, but to no avail. I run into the same issue when triggering from CLI, so I'm fairly sure it's an issue with authentication, however this is my Apps Script code in case it helps:
function test() {
const options = {
headers: {'Authorization': 'Bearer ' + ScriptApp.getIdentityToken()},
muteHttpExceptions: true
}
var result = UrlFetchApp.fetch('https://APP-ENGINE-URL.appspot.com', options);
Logger.log(result);
}
And the manifest file:
{
"timeZone": "Europe/London",
"dependencies": {
},
"exceptionLogging": "STACKDRIVER",
"runtimeVersion": "V8",
"oauthScopes": ["openid", "https://www.googleapis.com/auth/script.external_request"]
}
Any help on this is super appreciated! Never posted here before, but pretty desperate and couldn't find anyone with this exact problem on SO.