I need a clear, technically detailed article that walks an intermediate-level mobile developer through implementing FIDO2 passwordless authentication with Keycloak on both iOS and Android. The piece must read like a hands-on workshop: each phase of configuration and coding should build naturally on the previous one, so a reader can follow along and have a working demo by the end. Core expectations • Step-by-step tutorial: from spinning up or extending an existing Keycloak realm to registering a device and performing the first successful passwordless login. • Practical code examples: show the exact mobile-side calls that generate, store, and use FIDO2 credentials as well as the Keycloak configuration snippets that enable the flow. Include companion screenshots or CLI output whenever they clarify a step. Structure and depth Begin with a short overview of FIDO2 in the Keycloak context, then dive straight into environment prerequisites and Keycloak settings. Each major step—such as setting up WebAuthn policies, creating the client, configuring the credential manager, and handling fallback flows—should be its own section with clearly labeled code blocks and concise explanations. Wrap up with troubleshooting tips and pointers to official docs or SDK references. The tone should stay approachable yet precise; assume the reader knows their way around mobile projects and Keycloak basics but has not tackled passwordless auth before. I will consider the article complete when the instructions can be followed verbatim on a fresh Keycloak install to log in from both an iOS and an Android test app without ever typing a password, and all sample code compiles without modification.