How to select account in Google App Scripts for users with multiple accounts?

Question

For users that are logged into multiple accounts, how can a script let the user pick an account? For example, Gmail, Google Drive, etc. provide a way for the user to select which account to use with a selectable option on the top-right of the page:

How can developers implement a similar mechanism?

Answer 1

There seems to be no way to do that with Google Apps Script libraries - GAS just uses the current primary account. Also, unfortunately, the API Client Library and thus Google Sign-In for websites don't work inside GAS web apps because of the sandbox frame. You could write your own or use some existing OAuth implementation to authenticate with Google but I found a much much simpler solution using Auth0 Lock with only a Google Connection (using the popup method because the redirect method doesn't work within the sandbox frame).