code: def _is_compact_jws(self, jws):
          
          try:
              jwt = JWSig().unpack(jws)
          except Exception as err:
              logger.warning('Could not parse JWS: {}'.format(err))
              return False
  
          if "alg" not in jwt.headers:
              return False
  
          if jwt.headers["alg"] is None:
              jwt.headers["alg"] = "none"
  
          if jwt.headers["alg"] not in SIGNER_ALGS:
              logger.debug("UnknownSignerAlg: %s" % jwt.headers["alg"])
              return False
  
          self.jwt = jwt
          return True
docs: Check if we've got a compact signed JWT
  
          :param jws: The message
          :return: True/False