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libfido2
Provides library functionality for FIDO2, including communication with a device over USB or NFC.
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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
It's not extremely difficult at all to implement these! Heck, even at Google we use LibFido2 which is a free-to-use library (you can find it here if you want: https://github.com/Yubico/libfido2). Of course Google's version is a bit different and the creator of LibFido2 now works here, but all of these 2FA methods aren't particularly difficult to implement in the sense that most of the work (libraries, standards, exact specifications) is already done.