I am not sure if this is what you are asking, but by default this class uses sessions to store access tokens and secrets. If you want to access API from offline scripts when the user is not present, sessions will not do for recovering retrieved tokens.
You need to store the obtained tokens and restore them, or use a sub-class that stores the tokens on a persistent storage container, like a database.
There are sub-classes for storing the tokens in databases, like for instance MySQL.
Read this article to learn how to implement a client that stores and retrieves tokens for offline usage:
phpclasses.org/blog/package/7700/po
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