Werk #18995: Fix Unregistered YubiKey Authentication Crash

Component	Core & setup
Title	Fix Unregistered YubiKey Authentication Crash
Date	Feb 24, 2026
Level	Trivial Change
Class	New Feature
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.6.0b1 Not yet released Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk Cloud (CCE), Checkmk MSP (CME) 2.5.0b1 Not yet released Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk Cloud (CCE), Checkmk MSP (CME) 2.4.0p23 Not yet released Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk Cloud (CCE), Checkmk MSP (CME)

Fixed an issue where the authentication process would crash in certain circumstances if an unregistered YubiKey was used for two-factor authentication (2FA).

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