def METHOD_NAME(self, otter_config, assignment):
    """
    Takes a path to Google Service Account credentials stored in this plugin's config as key
    ``credentials_json_path`` and extracts the data from that file into the plugin's config as key
    ``service_account_credentials``.
    Args:
        otter_config (``dict``): the parsed Otter configuration JSON file
        assignment (``otter.assign.assignment.Assignment``): the assignment configurations if 
            Otter Assign is used
    """
    if assignment is not None:
        curr_dir = os.getcwd()
        os.chdir(assignment.master.parent)
    cfg_idx = [self.IMPORTABLE_NAME in c.keys() for c in otter_config["plugins"] if isinstance(c, dict)].index(True)
    creds_path = otter_config["plugins"][cfg_idx][self.IMPORTABLE_NAME]["credentials_json_path"]
    with open(creds_path, encoding="utf-8") as f:
        creds = json.load(f)
    otter_config["plugins"][cfg_idx][self.IMPORTABLE_NAME]["service_account_credentials"] = creds
    if assignment is not None:
        os.chdir(curr_dir)