Function auth_layer 

pub async fn auth_layer(
    __arg0: State<AuthConfig>,
    req: Request<Body>,
    next: Next,
) -> Response

Stackable middleware function: gate /v1/* requests on a bearer token when one is configured. /health and /metrics are always open so probes and scrapers don’t need credentials. /playground is likewise open when the route is enabled: it serves an inert HTML shell, and evaluation plus /playground/api/* model controls remain gated (the UI collects an optional API key for those calls).