def _build_tls_unknown_ca_alert(version):
    """
    Builds a TLS alert record for an unknown CA.
    """
    ver_maj, ver_min = TLS_PROTOCOL_VERSIONS[version]
    severity_fatal = 0x02
    description_unknown_ca = 0x30
    msg = struct.pack(">BB", severity_fatal, description_unknown_ca)
    msg_len = len(msg)
    record_type_alert = 0x15
    record = struct.pack(">BBBH", record_type_alert, ver_maj, ver_min, msg_len) + msg
    return record

    Builds a TLS alert record for an unknown CA.
    
lib/urllib3/contrib/_securetransport/low_level.py