To encrypt a secret:
./2fa add testing john@example.com my-random-2fa-secret-string
The encrypted 2fa secret was saved in ~/.2fa/testing.
To decrypt a secret:
./2fa code testing
2fa code (testing): 123456
The 2fa code is printed on screen.
2fa tutorial: https://etherarp.net/google-authenticator-without-a-phone/