Passkeys have recently emerged as a passwordless authentication mechanism, yet their usability in captive portals remains unexplored. This paper presents an empirical, comparative usability study of passkeys and passwords in a Wi-Fi hotspot using a captive portal. We conducted a controlled laboratory experiment with 50 participants following a split-plot design across Android and Windows platforms, using a router implementing the FIDO2CAP protocol. Our results show a tendency for passkeys to be perceived as more usable than passwords during login, although differences are not statistically significant. Independent of the authentication method, captive portal limitations negatively affected user experience and increased error rates. We further found that passkeys are generally easy to configure on both platforms, but platform-specific issues introduce notable usability challenges. Based on quantitative and qualitative findings, we derive design recommendations to improve captive portal authentication, including the introduction of usernameless authentication flows, improved captive portal detection mechanisms, and user interface design changes.

翻译：通行密钥（Passkeys）近期作为一种无密码认证机制出现，但它们在封闭式门户（Captive Portal）中的可用性尚未被探索。本文通过一项实证对比研究，评估了在Wi-Fi热点环境中使用封闭式门户时，通行密钥与密码的可用性差异。我们采用裂区设计（Split-plot Design），在Android与Windows双平台环境下组织50名受试者进行受控实验室实验，实验路由器实现了FIDO2CAP协议。结果表明，登录时通行密钥的感知可用性倾向于优于密码，但差异未达统计显著性。与认证方法无关，封闭式门户的限制对用户体验产生负面影响并提高了错误率。进一步研究发现，通行密钥在两平台上的配置过程普遍简便，但特定平台问题引入了显著的可用性挑战。基于定量与定性分析结果，我们提炼出改进封闭式门户认证的设计建议，包括引入无用户名认证流程、优化封闭式门户检测机制以及用户界面设计改进。