Using YubiKey as a One-Time-Password Token
YubiKeys as OTP Tokens can be used anywhere a Duo passcode is accepted; this includes all web browsers as well as non-web integrations. In order to use a YubiKey as an OTP Token, it must first be programmed. This is a complicated procedure. All modern browsers support FIDO2, so we highly encourage you to self-register your YubiKey.
If you still want to use your YubiKey as an OTP token, email calnet-admin@berkeley.edu.
For a more in-depth discussion of YubiKeys, see Yubico OTP vs. U2F and Configuring YubiKeys for OTP use with Duo