CVE-2026-59157: webhookd: Unrestricted HTTP Header to Shell Variable Injection

Before 1.22, if the Basic Auth (htpasswd) middleware was not configured, all incoming HTTP headers were blindly forwarded to the webhook script execution environment as shell variables. While the Basic Auth middleware correctly strips the authentication header (X-WebAuthn-User) from the incoming request before conditionally re-injecting it on successful authentication, disabling Basic Auth left the system vulnerable if deployed behind an unhardened reverse proxy.