What this tiny library does is it computes one time passwords, given the master password. It's basically the same computation Google Authenticator or Microsoft Authenticator do, given the master password. It means that you can either implement your own client or even your own server side authentication that would be compatible with existing authenticators (including the two).
What's interesting here is that the implementation is really, really tiny and has 0 dependencies. Usually, people implement TOTP using two dependencies:
- to handle the base32 encoding (master keys are usually provided in base32 encoding
- to handle the hmacsha1 to calculate actual codes