code: static CertStore getInstance(AccessDescription ad) {
          if (!ad.getAccessMethod().equals((Object)
                  AccessDescription.Ad_CAISSUERS_Id)) {
              return null;
          }
          GeneralNameInterface gn = ad.getAccessLocation().getName();
          if (!(gn instanceof URIName)) {
              return null;
          }
          URI uri = ((URIName) gn).getURI();
          try {
              return URICertStore.getInstance
                  (new URICertStore.URICertStoreParameters(uri));
          } catch (Exception ex) {
              if (debug != null) {
                  debug.println("exception creating CertStore: " + ex);
                  ex.printStackTrace();
              }
              return null;
          }
      }
docs: Creates a CertStore from information included in the AccessDescription
  object of a certificate's Authority Information Access Extension.