def METHOD_NAME(self):
    """Download metadata jcat signature"""
    if self.custom_url is None:
        metadata_url = METADATA_URL
    else:
        metadata_url = self.custom_url
    cmd_metadata = [
        "curl",
        "-fL",
        "-o",
        f"{self.metadata_file}.jcat",
        "--",
        f"{metadata_url}.jcat",
    ]
    p = subprocess.Popen(cmd_metadata)
    p.wait()
    if p.returncode != 0:
        raise Exception("fwupd-qubes: Downloading metadata file failed")
    if not os.path.exists(f"{self.metadata_file}.jcat"):
        raise FileNotFoundError(
            "fwupd-qubes: Downloaded metadata file does not exist"
        )
    environ = os.environ.copy()
    environ["LC_ALL"] = "C"
    cmd_info = ["jcat-tool", "info", f"{self.metadata_file}.jcat"]
    info_stdout = subprocess.check_output(cmd_info, env=environ).decode()
    info_id_line = [line for line in info_stdout.splitlines() if "ID:" in line]
    if info_id_line:
        info_id = info_id_line[0].split(":", 1)[1].strip()
    else:
        info_id = None
    if info_id and info_id != os.path.basename(metadata_url):
        # fetch the file referenced in jcat, to workaround CDN being few
        # hours out of sync
        self.custom_url = os.path.dirname(metadata_url) + "/" + info_id
    cmd_export = [
        "jcat-tool",
        f"--prefix={FWUPD_VM_METADATA_DIR}/",
        "--",
        "export",
        f"{self.metadata_file}.jcat",
    ]
    p = subprocess.Popen(cmd_export, stdout=subprocess.PIPE, env=environ)
    stdout, _ = p.communicate()
    if p.returncode != 0:
        raise Exception("fwupd-qubes: Extracting jcat file failed")
    # rename extracted files to match jcat base name, instead of "ID"
    # inside jcat
    for line in stdout.decode("ascii").splitlines():
        if not line.startswith("Wrote "):
            continue
        path = line.split(" ", 1)[1]
        base_path, ext = os.path.splitext(path)
        if base_path == self.metadata_file:
            continue
        new_path = f"{self.metadata_file}{ext}"
        os.rename(path, new_path)