yubikey 5 系列的容量：
OTP - this application can hold two credentials. However, Yubico OTP, one of the most popular kinds of credentials to put in this app, can be registered with an unlimited number of services.
FIDO U2F - similar to Yubico OTP, the U2F application can be registered with an unlimited number of services.
FIDO2 - the YubiKey 5 can hold up to 25 discoverable credentials in its FIDO2 application.
OATH (Yubico Authenticator) - the YubiKey 5's OATH application can hold up to 32 OATH-TOTP credentials (AKA authenticator app codes).
*PIV - the YubiKey 5's PIV (smart card) application has 24 slots, each of which can hold one certificate and its corresponding private key (click here for further information).
*†OpenPGP - the YubiKey 5's OpenPGP application can hold up to three OpenPGP private keys, one for encryption, one for signing, and one for authentication.https://support.yubico.com/hc/en-us/articles/360013790319-How-many-accounts-can-I-register-my-YubiKey-with-