Sign arbitrary data with your SSH keys

Ledger/Trezor have solved this since ~2016. I have a Ledger that has a private key inside and using a small open source tool (https://github.com/romanz/trezor-agent) I can SSH into machines, sign random data and Github commits and FIDO authenticate into several websites. All of that and knowing that these devices offer some of the best security out there.

Hardware devices like the crypto wallets are a pretty good solution (no pun intended), imho. Both very convenient and very secure. I like the minimalism of something like the Trezor, no battery, tiny B/W display and two hardware buttons. Plug in, click button to confirm signing, done.

FIDO2 is even better because SSH supports it natively, so there's no setup at all.