Sources

• Ledger Security Key app: https://support.ledger.com/article/12350325732893-zd
• LedgerHQ/app-security-key: https://github.com/LedgerHQ/app-security-key
• app-ssh-agent (deprecated, points to alternatives): https://github.com/LedgerHQ/app-ssh-agent
• OpenPGP app user guide: https://github.com/LedgerHQ/app-openpgp/blob/develop/doc/user/app-openpgp.rst
• SSH via OpenPGP card app (Ledger blog): https://dud225.github.io/LedgerHQ.github.io/ssh-with-openpgp-card-app/
• age-plugin-fido2-hmac: https://github.com/olastor/age-plugin-fido2-hmac
• trezor-agent (hardware SSH/GPG/age agent family): https://github.com/romanz/trezor-agent