State of Passkey Authentication in the Wild: A Census of the Top 100K sites

TL;DR

This paper introduces Fidentikit, a heuristic-based crawler, to measure passkey adoption across the top 100,000 websites, revealing that adoption correlates with site popularity and often relies on external identity providers.

Contribution

The paper presents Fidentikit, a novel browser-based crawler with 43 heuristics, and provides the first large-scale census of passkey adoption on major websites.

Findings

Higher adoption on popular sites

Dependence on external identity providers

Limited native passkey implementations

Abstract

Passkeys -- discoverable WebAuthn credentials synchronised across devices are widely promoted as the future of passwordless authentication. Built on the FIDO2 standard, they eliminate shared secrets and resist phishing while offering usability through platform credential managers. Since their introduction in 2022, major vendors have integrated passkeys into operating systems and browsers, and prominent websites have announced support. Yet the true extent of adoption across the broader web remains unknown. Measuring this is challenging because websites implement passkeys in heterogeneous ways. Some expose explicit "Sign in with passkey" buttons, others hide options under multi-step flows or rely on conditional mediation, and many adopt external mechanisms such as JavaScript libraries or OAuth-based identity providers. There is no standardised discovery endpoint, and dynamic, JavaScript-heavy pages complicate automated detection. This paper makes two contributions. First, we present Fidentikit, a browser-based crawler implementing 43 heuristics across five categories - UI elements, DOM structures, WebAuthn API calls, network patterns, and library detection - developed through iterative refinement over 1,500 sites. Second, we apply Fidentikit to the top 100,000 Tranco-ranked domains, producing the first large-scale census of passkey adoption. Our results show adoption strongly correlates with site popularity and often depends on external identity providers rather than native implementations.