docs: comment cache layer

gateway/src/api/cache_layer.rs

@@ -46,6 +46,10 @@ impl CacheManagement for CacheManager {
     }
 }
 
+/// The purpose of this layer is to cache the returned JWT token returned by calls to
+/// the auth endpoints that convert a cookie/api-key to a JWT: '/auth/key' and '/auth/session'.
+/// The layer will first check if the key/cookie-id is cached, if it is return it, if it isn't
+/// let the request go through, extract the JWT on the way back and cache it.
 #[derive(Clone)]
 pub(crate) struct CacheLayer<F> {
     pub(crate) cache_manager: Arc<Box<dyn CacheManagement>>,