This is a convenient hook point is subclasses want to do this differently, e.g. by farming the support-doc-fetching out to some worker processes.
Previously the delegation check was throwing a ConnectionError because it could not fetch the support document.
Because the audience can be specified at different locations (ie. at instanciation time and when calling the "verify" method), we need to be sure that the overwritting works like expected. This tests the different possible scenarios for the local verifier.