'Return the tokens needed to authenticate the access to any API the
service might provide. The return value will be a dictionary with the
token type name as key and the token value.
instance must be a UserSocialAuth instance.'

@classmethod
def tokens(cls, instance):

    if (instance.extra_data and ('access_token' in instance.extra_data)):
        return {'access_token': instance.extra_data['access_token']}
    else:
        return {}
