def METHOD_NAME(source_parameters) -> tuple[str, str] | None:
    """Return the basic authentication credentials, if any."""
    if private_token := source_parameters.get("private_token", ""):
        return private_token, ""
    username = source_parameters.get("username", "")
    password = source_parameters.get("password", "")
    return (username, password) if username or password else None