docs: def pick(self, acr=None):
          """
          Given the authentication context find zero or more authn methods
          that could be used.
  
          :param acr: The authentication class reference requested
          :return: An URL
          """
  
          if acr is None:
              # Anything else doesn't make sense
              return self.db.values()
          else:
              return self._pick_by_class_ref(acr)