This describes how to migrate from cEzyOauth2 while using the Goa library as described in Oauth2 for Apps Script in a few lines of code (which you should read first for background).
The library, cGoa, is available under this project key.
Goa is compatible with cEzyOauth2, and can use existing credentials and tokens that have been created by cEzyOauth2. The redirect URI will have changed and will need to be updated in the app dashboard as advised by the consent dialog when you get one.
The patterns for Goa are much simpler. I converted gasGit, which needs 2 token flows (one for drive, another for github) in a few minutes. There was no need to reinitialize the credentials since they are the same structure. After deleting all the ezyoauth2 stuff, the doGet pattern became. For more details on multiple Oauth2 see Multiple oAuth2 authentication packages
Next I needed a new version of getAccessToken() which I had written to pick up tokens inside the gasGit code.
Finally, I rewrote the the setOneTimeProperties - although not needed for this, they may be in the future. Once I run these and provoke a consent dialog, I'll need to update the redirect URI in the dev console.
Services > Desktop Liberation - the definitive resource for Google Apps Script and Microsoft Office automation > OAuth2 for Apps Script in a few lines of code >