GetPermittedForReferenceGrantFrom takes a ReferenceGrant From (a namespace, group, and kind) and returns a map from a namespace to a slice of ReferenceGrant Tos.

NewRefCheckerForRoute returns a RefChecker for the provided route and backendRef.

TLSVerifyDepthKey is the key used to store the tls verify depth.

RefChecker is a wrapper type that facilitates checking whether a backendRef is allowed by a referenceGrantTo set.