The answer depends on what option each application vendor and service provider offers users to address such a situation. It is common practice that the application or service may offer options to temporarily disable the need for the YubiKey Authentication, and fallback to one-factor authentication for certain duration (such as a day). Other applications may provide temporary OTPs over other communication channels, like SMS or email. Some applications may even support backup mobile tokens. But again, all these options need to be implemented by the application vendor or service provider in a way that suits their security requirements. Check with the application or service provider to see how they handle the situation where your YubiKey is unavailable.
Posted in: General Support Questions