triggered by https://stackoverflow.com/questions/70607615/varnish-how-to-check-jwt-signature-using-digest-vmod

Passes for our own code, have not looked at frozen itself yet

Ref https://gitlab.com/uplex/varnish/libvmod-frozen/issues/1

ref: 0c74d1b99f1f43fc99725fe14322760afa7858ee