This describes how to get and access token from the Goa library as described in Oauth2 for Apps Script in a few lines of code (which you should read first for background).
If you have initialized the credentials as described in Goa Setup, and gone through the process of the Goa Authentication dialog you are now ready to use the token or refreshed tokens with no further dialogs required.
This example does a query using the reddit API.
As described in Authentication dialog, you can simply leave the doGet() dialog in place instead of using this pattern, but using this simplified pattern allows you to unpublish the web app.
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Learning Apps Script, (and transitioning from VBA) are covered comprehensively in my my book, Going Gas - from VBA to Apps script, All formats are available from O'Reilly, Amazon and all good bookshops. You can also read a preview on O'Reilly
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