SaveCredentialsFile() does not store anything

[db0]

Calling the SaveCredentialsFile() method with a filename does nothing

I followed to calls inside until oauth2client.client.Storage.locked_put at which point I see:

    def locked_put(self, credentials):
        """Write a credential.

        The Storage lock must be held when this is called.

        Args:
            credentials: Credentials, the credentials to store.
        """
        raise NotImplementedError

I also see that oauth2client is deprecated for a while now. Is this a functionality that was removed or am I doing something wrong?