I have a browser extension which is scraping the threadId from the URL when the user is reading an email in Gmail, and is using this threadId to fetch circumstantial data using the Google Apps Script API.
The extension do however not know which of maybe several Google accounts are reading this message; it knows only the URL to my Apps Script webapp and the threadId. So when it executes the fetch, the webapp will the interpret request as coming from the default user session, which in some cases is wrong and will thus result in an null when executing GmailApp.getThreadById(e.parameter.threadId).
So what I am wondering is whether it is possible to specify what Google account to use when querying the webapp. Are there any possibilities other than asking the user to log off all other accounts and set the current one as default?
Unfortunately Google Apps Script does not have good support for multiple logins. See this page for more information.