Function jwks_builder 

pub fn jwks_builder(
    config: &AppConfig,
    keys: Option<&JwtKeys>,
    fetch: impl Fetch + 'static,
) -> Option<JwksBuilder>

The JWKS PGRST_JWT_JWKS_URL names, to be fetched through fetch, or None when it is not set.

keys are the ones parsed from PGRST_JWT_SECRET, which stay accepted beside the fetched ones. Every host builds its Jwks here, so that the URL, the refresh interval and how the two sources combine are read the same way everywhere; the host adds what only it has (a store, a task).