Authenticator with TOTP support

[stcarrez]

We can use akt as an authenticator with TOTP support (https://www.rfc-editor.org/rfc/rfc6238).

The new auth command has two modes. A first mode where it registers an otpauth URI with a shared secret.
The URI is registered as follows:

akt auth auth.akt otpauth://totp/GitHub:stcarrez?secret=XXXXXXXXXXXXX&issuer=GitHub

Then, to get the authenticate code, the auth command is used and we give the name of the issuer.

akt auth auth.akt GitHub

References:

• https://github.com/google/google-authenticator/wiki/Key-Uri-Format
• https://docs.yubico.com/yesdk/users-manual/application-oath/uri-string-format.html