code: def _get_principal(self, principal_arn):
          
          if ':cert/' in principal_arn:
              certs = [_ for _ in self.certificates.values() if _.arn == principal_arn]
              if len(certs) == 0:
                  raise ResourceNotFoundException()
              principal = certs[0]
              return principal
          else:
              # TODO: search for cognito_ids
              pass
          raise ResourceNotFoundException()
docs: raise ResourceNotFoundException