def METHOD_NAME():
    """
    Returns the path to the arc proxy file.
    """
    if "X509_USER_PROXY" in os.environ:
        return os.environ["X509_USER_PROXY"]
    # resolution order as in http://www.nordugrid.org/documents/arc-ce-sysadm-guide.pdf
    tmp = "/tmp"
    for v in ["TMPDIR", "TMP", "TEMP"]:
        if os.getenv(v):
            tmp = os.environ[v]
            break
    return os.path.join(tmp, "x509up_u{}".format(os.getuid()))