python3-mintotp is a minimalist implementation of TOTP.

You have probably seen how some obnoxious websites are not satisfied
with you just entering a correct username and password to log in.
They require something called "one-time pass", which is a seemingly
random combination of 6 alphanums.

mintotp is a tiny but self-contained implementation of those OTP
codes, including a python library and a command-line utility.

Use it just like
echo "<your-seed>" | mintotp
or mintotp < your-seed-file

Of course, you need to store the seed somewhere, preferrably in an
encrypted GnuPG file.