Function auth_begin 

pub fn auth_begin(
    owner: String,
    webauthn: &State<Option<WebauthnState>>,
    store: &State<CeremonyStore>,
    cookies: &CookieJar<'_>,
    pool: &State<DbPool>,
) -> Result<Json<RequestChallengeResponse>, Status>

Sign in, step 1 (POST /admin/passkeys/auth/begin?owner=): begins a passkey authentication for the named owner, seeded by that owner’s enrolled passkeys. Returns the WebAuthn RequestChallengeResponse for navigator.credentials.get() and stashes the ceremony state. 404 if the owner has no enrolled passkeys (admin identities are not treated as secret — the public deployment sits behind an Anubis proxy and the admin set is small), 503 if disabled.