I was unable to get authenticate.js to work. Browser would hang on redirect to localhost (ERR_CONNECTION_REFUSED). Attempted many things: changing firewall settings, localhost page settings, editing authenticate.js. After two days of attempting to learn how to code this myself, I realized Google provided an example on the page you linked, so I tried it and it worked in lieu of autheticate.js.
Consider rewording the authenticate directions as follows and direct users to use the Google index.js (or replicate herein).
After creating the OAuth2.0 Client ID, click the download button to the FAR right of the list item in the OAuth2.0 Client ID table here: https://console.cloud.google.com/apis/credentials, and save as MagicMirror/modules/MMM-GoogleTasks/credentials.js. Google's directions imply the file has been downloaded by the process of creating the Client ID (it hasn't).
I was unable to get authenticate.js to work. Browser would hang on redirect to localhost (ERR_CONNECTION_REFUSED). Attempted many things: changing firewall settings, localhost page settings, editing authenticate.js. After two days of attempting to learn how to code this myself, I realized Google provided an example on the page you linked, so I tried it and it worked in lieu of autheticate.js.
Consider rewording the authenticate directions as follows and direct users to use the Google index.js (or replicate herein).
Authenticate and retrieve Google Task List IDs
Go here: https://developers.google.com/tasks/quickstart/nodejs and perform everything on the page: