optfeature "support for OpenSSH private key encryption" dev-python/bcrypt
optfeature "support for key exchange and authentication with U2F/FIDO2 security keys" dev-python/fido2
optfeature "support for accessing PIV keys on PKCS#11 security tokens" dev-python/python-pkcs11
optfeature "support for GSSAPI key exchange and authentication on UNIX" dev-python/gssapi
optfeature "if you have a version of OpenSSL older than 1.1.1b installed and you want support for Curve25519 key exchange, Ed25519 keys and certificates, or the Chacha20-Poly1305 cipher" dev-python/libnacl
optfeature "support for UMAC cryptographic hashes" dev-python/libnettle
optfeature "support for X.509 certificate authentication" dev-python/pyopenssl